Method for preventing R-angle bridging of honeycomb sandwich

Abstract

The present application belongs to the field of honeycomb forming, and relates to a method for preventing R-angle bridging of a honeycomb sandwich part. The method comprises the following steps: cutting prepreg: cutting honeycomb lower skin prepreg and honeycomb upper skin prepreg into square zigzag shapes with anti-skid belt tethering area; the space between the square zigzags is used for tethering the anti-skid belt; laying the pieces in turn in the order of blank pages, and then carrying out honeycomb cutting, layering, paste vacuum bagging and curing.

Description

Technical Field

[0001] This invention belongs to the field of honeycomb molding and relates to a method for preventing bridging at the R-angle of honeycomb sandwich components. Background Technology

[0002] The application of composite materials mainly stems from their advantages such as high specific strength, specific stiffness, corrosion resistance, fatigue resistance, and designability, especially in the aerospace field where they replace traditional metal parts to achieve weight reduction and performance improvement. Among them, honeycomb sandwich components achieve extremely high bending strength at the cost of very low weight. It is essentially an engineering implementation of an "I-beam" structure—two thin and strong panels bear tensile and compressive loads, and the honeycomb core in the middle separates the panels, significantly increasing the moment of inertia of the cross section.

[0003] Large-area flat curved surfaces such as aircraft wings, tail fins, floors, and fairings utilize honeycomb structures to achieve significantly higher rigidity than solid composite material components of the same weight, meeting load-bearing and deformation resistance requirements with almost no increase in weight.

[0004] A crucial prerequisite for achieving the desired mechanical properties in large-sized honeycomb sandwich components without increasing weight is high internal quality requirements, especially the absence of bridging at the transition sections between the honeycomb and the inner and outer skins. "R-corner bridging" is a typical defect in the molding of composite sandwich components. It refers to a situation where, at the radius (radius) of the part, the prepreg does not conform to the mold's radius but instead directly "shortcuts" by connecting the two sides, creating voids or areas with insufficient resin. Once bridging occurs, the strength of the radius decreases significantly, making it prone to porosity, delamination, and even becoming the starting point for part failure.

[0005] For a type of high-thickness honeycomb sandwich component with large chamfers, to prevent slippage during curing, a whole anti-slip strip is needed to "tether" the prepreg around the top and bottom panels of the honeycomb during layup. However, if the prepreg has poor ductility and the part is large, the area of ​​prepreg bound by the anti-slip strip is also large. During heat curing, the anti-slip strip may "over-bind" the prepreg, causing the prepreg in the radius corner area to not fully adhere to the mold, resulting in radius corner bridging. Summary of the Invention

[0006] Purpose of the invention: The present invention provides a method for preventing bridging at the R-angle of a honeycomb sandwich component, which can both prevent slippage of the honeycomb with large chamfers and high thickness, and also avoid bridging caused by the transition anchoring of the anti-slip strip.

[0007] Technical solution: A method for preventing bridging at the radius (R) angle of a honeycomb sandwich component is provided, comprising: Cutting the prepreg: The prepreg for the lower and upper honeycomb skins and the area where the anti-slip strip is fastened are cut into a square serrated shape; the space between the square serrations is used to fasten the anti-slip strip. Lay the sheet material flat in sequence according to the material page order, and then perform honeycomb cutting, layering, vacuum bag making, and curing.

[0008] Furthermore, the distance between the square serrations is between 300-400mm.

[0009] Further, the honeycomb structure is cut, including: Make sure one side of the honeycomb is completely adhered to the tape; With the tape side facing up, place the honeycomb flat on the vacuum table, turn on the machine tool's negative pressure, and make the tape adhere firmly to the honeycomb. Unload the negative pressure, flip the honeycomb so that the tape side is facing down, and place the honeycomb flat on the vacuum table; Align one long edge of the cell with the baseline on the table, or use laser projection for positioning. Turn on the machine tool's negative pressure, adsorb the honeycomb onto the vacuum platform, and confirm that the honeycomb is flat and firmly bonded; Perform honeycomb cutting according to the CNC program for honeycomb cutting; Mark the honeycomb pattern number, version number, and product number on the single-sided tape, and then stick the single-sided tape to the honeycomb surface.

[0010] Further, lay-up includes: (1) Laser projector positioning: Positioning is achieved by scanning the reference points on the fixture, the projection program is tested, and calibration is performed by scribing lines on the fixture; (2) Lay the first layer of prepreg on the molding mold according to the projection procedure. Before laying, peel off the protective film. When laying, stretch the prepreg straight and use a pressure roller or hand to push it from one end of the cloth. Lift the other end of the cloth by hand and let it fall gradually until the end as the pressure roller or hand pushes it down to remove all air bubbles. After laying, peel off the other layer of protective film. (3) Vacuum compaction at room temperature. Use a non-porous isolation membrane during the vacuuming process. Start timing after the vacuum bag reaches the pressure value. Set the vacuum pressure to -0.07 to -0.09 MPa and the duration to 30 to 40 minutes. After compaction, the compaction quality should be checked to ensure that there are no wrinkles or bridging.

[0011] (4) After laying the first layer of prepreg, lay the remaining prepreg. After laying 3 to 4 layers of prepreg, vacuum compaction is performed once. The method and layer requirements are the same as in steps (2) and (3) until the last layer of prepreg on the outer skin is laid. (5) Compact the material under vacuum at room temperature, using the same method as step (3); (6) Laying the honeycomb structure: The honeycomb structure should be laid as flat as possible to avoid stretching or compressing the cell, which could cause laying stress and lead to slippage of the cured honeycomb core. If the dimensions are out of tolerance after laying, adjustments should be made promptly. (7) After the honeycomb is laid, the first layer of prepreg material of the inner skin is laid, in the same way as step (2), and vacuum compacted at room temperature, in the same way as step (3). (8) Lay the remaining prepreg on the inner skin. After laying 3 to 4 layers of prepreg, vacuum compact it once. The method and layer requirements are the same as in steps (2) and (3) until the last layer of prepreg on the outer skin is laid.

[0012] (9) Perform pre-compaction as per step (3).

[0013] Furthermore, during positioning, the tool is placed at the center of the projection area, and the layup is performed with half the width of the projection line as the layup boundary.

[0014] Furthermore, the unidirectional fabric laying angle deviation is ±3°; the fabric laying angle deviation is ±5°; and the tolerance for the layup boundary and overlap position is ±3mm.

[0015] Further, curing includes: The entire part is placed in an autoclave for curing. Curing parameters are as follows: negative pressure not less than 0.07 MPa, positive pressure 0.2±0.02 MPa, heating and cooling rate 0.5-2℃ / min, pressurization rate 0.02-0.025 MPa / min; after heating to 120℃, hold at that temperature for 2±2 hours. After the isothermal period, begin cooling, with a cooling rate not exceeding 3℃ / min.

[0016] Furthermore, before cutting the prepreg, the method further includes: Tooling and material preparation.

[0017] Furthermore, the tooling preparation includes: Tooling requisition: Requisition tooling according to the tooling drawing number and check the tooling certificate of conformity; Use adhesive to fix the anti-slip strip to the corresponding area of ​​the molding mold. Put the molding mold and the anti-slip strip into the curing oven for curing. After curing, clean the glue nodules on the edges of the anti-slip strip.

[0018] Tooling inspection: Visually inspect the tooling, including whether the tooling surface is worn or corroded, and whether there are dents, scratches and rust on the tooling surface.

[0019] Beneficial effects: It effectively prevents relative slippage between the honeycomb core and the panel in the honeycomb sandwich component, ensures stress uniform transmission in the composite sandwich structure, avoids local stress concentration, and thus maintains the design load-bearing capacity. It effectively prevents bridging of the upper and lower panels of the honeycomb sandwich component in the R-corner area, avoids the formation of local rigidity abrupt change and stress concentration in the reinforced area, and prevents microcracks from easily generating and propagating under alternating loads; The ductility of the upper and lower honeycomb skin prepregs can be adjusted according to the tethering area of ​​the upper and lower honeycomb skin prepregs on the anti-slip strip. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the anti-slip strip's anchoring cross-section. 1-Forming mold, 2-Anti-slip strip, 3-Lower skin, 4-Honeycomb, 5-Upper skin.

[0022] Figure 2 This is a schematic diagram of the traditional prepreg anchorage area.

[0023] Figure 3 This is a schematic diagram of the prepreg anchorage area of ​​the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setups and methods set forth below, but covers any improvements, substitutions, and modifications to structures, methods, and devices without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description to avoid unnecessarily obscuring the invention.

[0026] In the description of this invention, it should be noted that the directions or positional relationships indicated by terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing and simplifying the invention, and should not be construed as limiting the invention. Furthermore, the use of ordinal numbers (e.g., "first and second," etc.) is for distinguishing objects and is not limited to this order, and should not be construed as indicating or implying relative importance.

[0027] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly, encompassing both direct connection and indirect connection via an intermediate medium. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0028] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0030] The main technical concept adopted in this invention is as follows: When honeycomb slippage occurs in composite honeycomb sandwich components, the slippage in the prepreg layer mainly concentrates at two interfaces: the weakest friction surfaces where the honeycomb adheres to the lower skin and the honeycomb adheres to the upper skin. These two interfaces inevitably slip during honeycomb slippage. Therefore, the method to prevent honeycomb slippage is to use anti-slip tapes to secure the prepregs at the top and bottom of the honeycomb. The core principle is to physically secure the prepregs of the upper and lower skins of the honeycomb with anti-slip tapes, enhancing the peel and shear resistance between the upper and lower skins and the honeycomb core, thereby preventing slippage of the upper and lower skins during the curing process. (See the schematic diagram.) Figure 1 .

[0031] The larger the area of ​​the anti-slip strip secured to the prepreg, the stronger the anti-slip ability of the prepreg in the upper and lower skins of the honeycomb structure. Generally, according to traditional methods, the prepreg in the upper and lower skins of the honeycomb structure is completely secured to the anti-slip strip according to its width and length. Figure 2During the process of laying prepreg on the molding die, vacuum pressure is applied to ensure the prepreg adheres to the die as much as possible. However, some gaps may still exist, which need to be eliminated by the positive pressure of the autoclave during curing. During the application of positive pressure during curing, the prepreg also needs a certain degree of ductility to achieve complete adhesion between the prepreg and the die. However, some high-modulus prepregs have poor ductility, especially in the radius (R) corners of honeycomb sandwich components. High-modulus prepregs and tooling cannot adhere completely to the die as intended. Furthermore, the edges of the prepregs on the upper and lower honeycomb skins are completely secured to the anti-slip strips, failing to provide a channel for adhesion between the prepreg and the die, thus creating a "bridging defect" in the radius (R) corners. In this case, it is necessary to appropriately reduce the securing force between the anti-slip strips and the prepreg to improve the adhesion between the high-modulus prepreg and the die. The final technical concept of this invention is to adjust the area of ​​the prepreg and the anti-slip strip fastening according to the extensibility of the honeycomb upper and lower skin prepregs, so as to not only prevent honeycomb slippage, but also ensure the fit between the honeycomb upper and lower skin prepregs and the molding mold.

[0032] Specific implementation steps of the present invention Step 1: Tooling Preparation (1) Tooling collection: Collect tooling according to tooling drawing number and check tooling certificate of conformity; (2) Use adhesive to fix the anti-slip strip to the corresponding area of ​​the molding mold, and put the molding mold and anti-slip strip into the curing oven for curing. After curing, clean the glue nodules on the edge of the anti-slip strip.

[0033] (3) Tooling inspection: Visually inspect the tooling, including whether the tooling surface is worn or corroded, and whether the tooling surface is dented, scratched or corroded.

[0034] Step 2: Material Preparation (1) Collect the corresponding prepreg and honeycomb according to the process instructions; (2) Low-temperature materials are thawed in an air-conditioned room. During the thawing process, the materials are kept sealed. Before opening the seal, ensure that no moisture is formed inside or outside the bag. (3) The pre-made materials are not allowed to be folded. They can be laid flat or rolled up with support for storage.

[0035] Step 3: Material preparation (a) Prepreg cutting (1) Press the material sheet and the corresponding program to use the correct prepreg CNC cutting. The cut material sheet should be marked with: product drawing number, layup number, angle, and fiber direction of the fabric. Among them, the honeycomb lower skin prepreg 3 and honeycomb upper skin prepreg 5 and the anti-slip belt tethering area are cut into square sawtooth shape. The distance between the square sawtooth is recommended to be between 300-400mm.

[0036] (2) Lay the sheets flat in the order of the sheet pages, and check the integrity of the sheets and the clarity and completeness of the markings.

[0037] (ii) Honeycomb cutting (1) Make one side of honeycomb 4 completely adhere to the tape; (2) With the tape side facing up, place the honeycomb 4 flat on the vacuum table, turn on the machine tool negative pressure, and make the tape adhere firmly to the honeycomb 4; (3) Unload the negative pressure, flip the honeycomb 4 so that the tape side is facing down, and place the honeycomb 4 flat on the vacuum table; (4) Align one long side of the honeycomb with the baseline on the table, or use laser projection for positioning. (5) Turn on the machine tool negative pressure, adsorb the honeycomb 4 onto the vacuum platform, and confirm that the honeycomb 4 is flat and firmly bonded; (6) Perform honeycomb cutting according to the CNC program for honeycomb 4-cutting; (7) Mark the drawing number, version number and product drawing number of honeycomb 4 on the single-sided tape, and stick the single-sided tape on the surface of honeycomb 4.

[0038] Step 4: Laying out layers (1) Laser projector positioning: Position the laser projector by scanning the reference point on the fixture, run the projection program for trial operation, and calibrate it by scribing the fixture. The fixture should be placed in the center of the projection area as much as possible, and the layup should be carried out with the width of the projection line as 1 / 2 of the layup boundary.

[0039] (2) Lay the first layer of prepreg on the molding die according to the projection procedure. Before laying, peel off the protective film. When laying, stretch the prepreg straight and use a roller or your hand to press it from one end of the fabric. Lift the other end of the fabric by hand and let it fall gradually to the end with the roller or your hand, removing all air bubbles. After laying, peel off the other layer of protective film. The unidirectional fabric laying angle deviation is ±3°; the fabric laying angle deviation is ±5°. The tolerance for the lay-up boundary and overlap position is ±3mm.

[0040] (3) Compact the vacuum bag at room temperature. Use a non-porous isolation membrane during the vacuuming process. Start timing after the vacuum bag reaches the pressure value. The vacuum pressure is -0.07 to -0.09 MPa, and the time is 30 to 40 minutes. After compaction, the compaction quality should be checked to ensure that there are no wrinkles or bridging.

[0041] (4) After laying the first layer of prepreg, lay the remaining prepreg. After laying 3 to 4 layers of prepreg, vacuum compact once. The method and layer requirements are the same as in steps (2) and (3) until the last layer of prepreg of the outer skin 3 is laid. (5) Compact the material under vacuum at room temperature, using the same method as step (3); (6) Lay out honeycomb 4. When laying out honeycomb 4, it should be laid as flat as possible to avoid stretching or compressing the honeycomb cells, which would cause laying stress and lead to slippage of the honeycomb core after curing. If the dimensions are out of tolerance after laying, adjustments should be made in time. (7) After the honeycomb 4 is laid, the first layer of prepreg material of the inner skin 5 is laid, in the same way as step (2), and vacuumed and compacted at room temperature, in the same way as step (3). (8) Lay the remaining prepreg of the inner skin 5. After laying 3 to 4 layers of prepreg, vacuum compaction is performed once. The method and layering requirements are the same as in steps (2) and (3) until the last layer of prepreg of the outer skin 5 is laid.

[0042] (9) Perform pre-compaction as per step (3).

[0043] Step 5: Make the final vacuum bag; (1) Paste vacuum bags, check the quality of vacuum bag pasting, and check that the vacuum nozzles are placed in the correct position and quantity; (2) Vacuum degree detection: The vacuum degree of the vacuum bag reaches 0.09MPa until the vacuum degree stabilizes. After 15 minutes, the vacuum source is turned off or shut off. The vacuum gauge reading should not drop by more than 0.017MPa within 5 minutes.

[0044] Step 6: Curing The entire part is placed in an autoclave for curing. Curing parameters are as follows: negative pressure not less than 0.07 MPa, positive pressure 0.2±0.02 MPa, heating and cooling rate 0.5-2℃ / min, and pressurization rate 0.02-0.025 MPa / min. After heating to 120℃, it is held at that temperature for 2±2 hours. After the temperature is maintained, cooling begins, with a cooling rate not exceeding 3℃ / min.

[0045] Step 7: Unmolding Insert the mold release wedge evenly into the gap between the edge of the part and the tooling. After ensuring that the edge of the part has been removed from the tooling, insert the mold release wedge evenly inward around the part. Do not use excessive force during operation.

[0046] Step 8: Mark Mark product drawing number, version number, serial number, and other information on the product; Step 9: Cutting Cut off the portion outside the allowance line along the product's edge.

[0047] The above detailed embodiments are a description of the present invention. It should not be considered that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A method of preventing R-angle bridging of a honeycomb sandwich member, characterized by, include: Cutting the prepreg: The prepreg of the lower honeycomb skin and the prepreg of the upper honeycomb skin are cut into square sawtooth shapes in the area where the anti-slip belt is fastened; The space between the square serrations is used to fasten anti-slip strips; Lay the sheet material flat in sequence according to the material page order, and then perform honeycomb cutting, layering, vacuum bag making, and curing.

2. The method according to claim 1, characterized in that, The distance between the square serrations is between 300-400mm.

3. The method according to claim 1, characterized in that, Cellular cutting includes: Make sure one side of the honeycomb is completely adhered to the tape; With the tape side facing up, place the honeycomb flat on the vacuum table, turn on the machine tool's negative pressure, and make the tape adhere firmly to the honeycomb. Unload the negative pressure, flip the honeycomb so that the tape side is facing down, and place the honeycomb flat on the vacuum table; Align one long edge of the cell with the baseline on the table, or use laser projection for positioning. Turn on the machine tool's negative pressure, adsorb the honeycomb onto the vacuum platform, and confirm that the honeycomb is flat and firmly bonded; Perform honeycomb cutting according to the CNC program for honeycomb cutting; Mark the honeycomb pattern number, version number, and product number on the single-sided tape, and then stick the single-sided tape to the honeycomb surface.

4. The method according to claim 3, characterized in that, Layers, including: (1) Laser projector positioning: Positioning is achieved by scanning the reference points on the fixture, the projection program is tested, and calibration is performed by scribing lines on the fixture; (2) Lay the first layer of prepreg on the molding mold according to the projection procedure. Before laying, peel off the protective film. When laying, stretch the prepreg straight and use a pressure roller or hand to push it from one end of the cloth. Lift the other end of the cloth by hand and let it fall gradually until the end as the pressure roller or hand pushes it down to remove all air bubbles. After laying, peel off the other layer of protective film. (3) Vacuum compaction at room temperature. Use a non-porous isolation membrane during the vacuuming process. Start timing after the vacuum bag reaches the pressure value. Set the vacuum pressure to -0.07 to -0.09 MPa and the duration to 30 to 40 minutes. After compaction, the compaction quality should be checked to ensure that there are no wrinkles or bridging. (4) After laying the first layer of prepreg, lay the remaining prepreg. After laying 3 to 4 layers of prepreg, vacuum compaction is performed once. The method and layer requirements are the same as in steps (2) and (3) until the last layer of prepreg on the outer skin is laid. (5) Compact the material under vacuum at room temperature, using the same method as step (3); (6) Laying the honeycomb structure: The honeycomb structure should be laid as flat as possible to avoid stretching or compressing the cell, which could cause laying stress and lead to slippage of the cured honeycomb core. If the dimensions are out of tolerance after laying, adjustments should be made promptly. (7) After the honeycomb is laid, the first layer of prepreg material of the inner skin is laid, in the same way as step (2), and vacuum compacted at room temperature, in the same way as step (3). (8) Lay the remaining prepreg on the inner skin. After laying 3 to 4 layers of prepreg, vacuum compact it once. The method and layer requirements are the same as in steps (2) and (3) until the last layer of prepreg on the outer skin is laid. (9) Perform pre-compaction as per step (3).

5. The method according to claim 4, characterized in that, During positioning, the tool is placed at the center of the projection area, and the layup is performed with half the width of the projection line as the layup boundary.

6. The method according to claim 4, characterized in that, The unidirectional fabric laying angle deviation is ±3°; the fabric laying angle deviation is ±5°; the tolerance for the layup boundary and overlap position is ±3mm.

7. The method according to claim 4, characterized in that, Curing, including: The entire part is placed in an autoclave for curing. Curing parameters are as follows: negative pressure not less than 0.07 MPa, positive pressure 0.2±0.02 MPa, heating and cooling rate 0.5-2℃ / min, pressurization rate 0.02-0.025 MPa / min; after heating to 120℃, hold at that temperature for 2±2 hours. After the isothermal period, begin cooling, with a cooling rate not exceeding 3℃ / min.

8. The method according to claim 1, characterized in that, Before cutting the prepreg, the method further includes: Tooling and material preparation.

9. The method according to claim 8, characterized in that, The tooling preparation includes: Tooling requisition: Requisition tooling according to the tooling drawing number and check the tooling certificate of conformity; Use adhesive to fix the anti-slip strip to the corresponding area of ​​the molding mold. Put the molding mold and the anti-slip strip into the curing oven for curing. After curing, clean the glue nodules on the edges of the anti-slip strip. Tooling inspection: Visually inspect the tooling, including whether the tooling surface is worn or corroded, and whether there are dents, scratches and rust on the tooling surface.

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