High-precision forming and processing method of double-curved surface honeycomb

Abstract

This invention provides a high-precision molding and processing method for hyperboloid honeycomb, belonging to the field of aerospace composite material manufacturing. The molding and processing method includes the following steps: First, a curved surface that ensures the honeycomb lattice direction is perpendicular to the lattice wall direction is identified as the molding surface, and the other surface is identified as the processing surface. Next, a mold consisting of a base layer and a removable layer is designed and manufactured, with the removable layer's profile fitting the molding surface. Then, pre-impregnated honeycomb material is laid on the removable layer and cured, ensuring the lower surface of the honeycomb precisely fits the profile and the lattice direction is correct. After curing, the removable layer with the honeycomb is transferred as a whole to a CNC machine tool for single-sided milling of the processing surface. Finally, the processed honeycomb and removable layer are transferred together to the bonding process. This invention achieves high-precision manufacturing of hyperboloid honeycomb through single-sided molding, single-sided processing, and overall transfer, effectively controlling the lattice direction and lattice wall direction, improving material utilization and product performance consistency.

Description

Technical Field

[0001] This invention relates to the field of aerospace composite material structural component manufacturing technology, and more specifically, to a high-precision molding and processing method for hyperboloid honeycomb. Background Technology

[0002] Composite materials, due to their high specific strength, high specific stiffness, strong designability, good fatigue fracture resistance, corrosion resistance, good dimensional stability, and ease of large-area integral molding, have become one of the most important structural materials in modern aerospace. Sandwich structures typically use high-density foam or honeycomb as core materials, which are highly efficient in reducing weight and impact resistance. Furthermore, antenna structures can be arranged within the sandwich layer to achieve functional and structural integration, making sandwich structures widely used.

[0003] With the continuous optimization of product structures, the shapes of honeycomb sandwich composite materials are becoming more complex and precise. To meet the shape requirements of products, the shape of the honeycomb core material inside some honeycomb sandwich structures is very complex. The shape precision of the honeycomb core material directly affects the final aerodynamic shape of the product, while the direction of the pores and the direction of the pore walls also directly affect the final mechanical properties of the product.

[0004] Existing honeycomb processing methods, which often involve machining a block-shaped blank, typically use two sides with hyperboloidal features. The first side is machined, and then the material is transferred to another mold for machining the second side. This method requires machining both sides of the product, and errors in the first side machining can transfer to a reference point, affecting the machining accuracy of the second side. The biggest problem with this method is that because machining is done on a single block of blank, the direction of the honeycomb cells and the direction of the cell walls cannot maintain a normal angle with the curved surface of the product. This affects the final mechanical properties of the product. Furthermore, as a flexible material, honeycomb is prone to deformation after machining, leading to deviations in surface accuracy and affecting the final appearance quality of the product. Summary of the Invention

[0005] (a) Technical problems to be solved The technical problems this invention aims to solve are: existing hyperboloid flexible honeycomb systems require double-sided processing, leading to issues such as processing accuracy deviations due to datum transfer and processing surface tolerances; inconsistencies between the cell wall direction and the surface normal due to the use of block blanks; and low utilization of honeycomb raw materials. Furthermore, because the honeycomb is a flexible material, removing the honeycomb material after processing and then assembling it can cause changes in the honeycomb surface due to localized dragging and pulling, thus making it impossible to effectively transfer the precision of the honeycomb processing to the bonding step.

[0006] (II) Technical Solution To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high-precision molding and processing method for hyperboloid honeycomb is provided, including the following steps: S1. According to the technical requirements of hyperboloid honeycomb, the surface that needs to be perpendicular to the direction of the honeycomb cells and the direction of the cell walls is determined as the forming surface, and the other surface is determined as the processing surface. Specifically, based on the design model and technical requirements of the final hyperboloid honeycomb product, an analysis is conducted. The complex surface that needs to be strictly perpendicular to the surface (i.e., along the normal direction of the surface) in the direction of the honeycomb cells and the direction of the cell walls is determined as the forming surface; then the other surface that needs to be finally formed, regardless of whether it is a complex surface, is determined as the processing surface.

[0007] S2. Design and manufacture a mold based on the shape of the molding surface. The mold includes a base layer, a removable layer, and a positioning structure. The surface of the removable layer fits the molding surface, and the positioning structure connects the removable layer and the base layer. Specifically, a special mold is designed and manufactured based on the mathematical model and shape of the molding surface determined in step S1. This mold adopts a unique modular design, including a base layer, a removable layer, and a positioning structure. The base layer, as the main load-bearing structure, provides overall rigidity and stability to the mold and is typically made of metal (such as aluminum or steel) or high-rigidity composite materials. The working surface of the removable layer is completely consistent with the mathematical model of the molding surface. This layer is separable from the base layer and has sufficient rigidity and dimensional stability to serve as the carrier for the honeycomb structure in subsequent processes. The positioning structure is used to achieve precise positioning and reliable connection between the removable layer and the base layer, and between the removable layer and the bonding mold in subsequent processes.

[0008] S3. Pre-impregnated honeycomb material is laid and fixed onto the surface of the removable layer to form a pre-formed assembly. The lower surface of the pre-impregnated honeycomb material is fully fitted to the surface of the removable layer, and the direction of the honeycomb cells and cell walls is aligned with the normal direction of the forming surface. The pre-formed assembly is then vacuum-sealed and cured. Specifically, honeycomb materials pre-impregnated with resin (such as epoxy resin or phenolic resin systems), such as aramid paper honeycomb, glass cloth honeycomb, or aluminum honeycomb, are selected. The pre-impregnated honeycomb material of calculated dimensions is laid and tightly adhered to the surface of the removable layer, ensuring that the lower surface of the honeycomb is fully fitted to the surface of the removable layer, and that the cell walls are naturally perpendicular to (i.e., along the normal direction) the forming surface. This step ensures that the direction of the honeycomb cells and cell walls is consistent with the product design requirements. On the mold with the honeycomb layer laid out, auxiliary materials such as release fabric, air-guiding felt, and vacuum bag film are laid and sealed. After vacuum sealing, a preformed component is obtained. The entire preformed component is placed in an autoclave or oven and cured by heating according to the curing curve of the prepreg honeycomb resin system (e.g., heating to 100℃~180℃, applying a vacuum negative pressure of -0.095MPa to -0.1MPa and maintaining it for a certain time). After curing, the lower surface of the honeycomb (i.e., the surface in contact with the removable layer) is precisely shaped into the required molding surface and is firmly bonded to the removable layer.

[0009] S4. After curing, the removable layer with the cured honeycomb is fixed as a whole on a CNC machine tool. The machining surface of the honeycomb is CNC machined to obtain the final designed hyperboloid honeycomb shape. Specifically, after curing, there is no need to remove the honeycomb from the removable layer. The removable layer with the cured honeycomb is directly installed and fixed on the CNC machine tool's worktable as a whole component through its positioning structure. At this time, the formed side of the honeycomb (the formed surface) is perfectly supported and protected by the removable layer. Then, the CNC machine tool performs high-speed milling and other CNC machining on the upper surface of the honeycomb (i.e., the surface opposite to the formed surface) according to the mathematical model of the machining surface. This process is single-sided machining, and the formed surface does not participate in cutting, completely avoiding the reference conversion error of double-sided machining. After machining, a honeycomb core material with a precise hyperboloid shape is obtained.

[0010] S5. Separate the processed hyperboloid honeycomb, along with the removable layer, from the base layer. Treat the removable layer and the hyperboloid honeycomb as a single unit, and position and transfer them to a bonding mold using a positioning structure for subsequent bonding. Specifically, after processing, separate the removable layer from the base layer. Using a uniform positioning structure (such as positioning holes) on the removable layer, accurately position the entire component and transfer it to the subsequent bonding mold or assembly jig. During the bonding process, the honeycomb achieves precise and stable positioning through the removable layer, thereby transferring the high-precision shape obtained in the processing steps to the final product without loss.

[0011] Preferably, in step S2, the removable layer is made of a composite material with a thickness of 0.5 mm to 3 mm.

[0012] Preferably, the composite material is fiberglass or carbon fiber laminate.

[0013] Preferably, the positioning structure is a positioning hole provided on the removable layer and the base layer, or a positioning hole provided on the removable layer and the bonding mold.

[0014] Preferably, in step S3, the pre-impregnated honeycomb material is a honeycomb of uniform thickness, and its thickness m satisfies the formula: m=n+(3~5) mm, where n is the distance offset from the molding surface to the point that can completely enclose the processing surface.

[0015] Preferably, in step S3, the curing process includes: laying auxiliary materials on a mold on which pre-impregnated honeycomb material has been laid to complete vacuum sealing, forming a pre-formed component with the mold, and then placing the pre-formed component into a vacuum chamber for heating and curing.

[0016] Preferably, the preimpregnated honeycomb material is one of aramid paper honeycomb, glass cloth honeycomb, or aluminum honeycomb, and its preimpregnated resin is an epoxy resin-phenolic resin system.

[0017] (III) Beneficial Effects The above-described technical solution of the present invention has at least the following advantages: 1. This invention employs a strategy combining single-sided forming and single-sided machining, completely eliminating the cumulative errors caused by datum conversion and reclamping in traditional double-sided machining. The accuracy of the formed surface is guaranteed by the mold, while the accuracy of the machined surface is guaranteed by a single clamping operation on a CNC machine tool. The two are linked through a unified detachable layer, resulting in a significant improvement in the final product's surface accuracy.

[0018] 2. This invention ensures that the direction of the honeycomb cell grid and the direction of the cell wall are always consistent with the direction of the normal to the curved surface on the molding surface by curing on the molding surface most relevant to the stress requirements of the product, thereby maximizing the mechanical properties of the honeycomb core material and improving structural efficiency.

[0019] 3. The present invention uses a prepreg honeycomb blank with approximately equal thickness, which is only slightly larger than the maximum thickness of the final product (adding a machining allowance), avoiding the removal of a large amount of material from large block blanks by milling, significantly improving the utilization rate of raw materials and reducing costs.

[0020] 4. This invention employs a detachable layer structure design, ensuring that the honeycomb remains attached to a precise, rigid "tray" throughout the entire process from molding and processing to transfer and bonding. This completely avoids deformation of the flexible honeycomb caused by handling and transportation between processes, achieving a seamless transfer of processing precision to the final product's bonding precision, resulting in excellent process stability. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, 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.

[0022] Figure 1 This is a schematic diagram of the manufacturing mold provided in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the processing area of ​​the cured honeycomb provided in an embodiment of the present invention.

[0024] The labels for the attached figures are as follows: 1. Base layer; 2. Removable layer; 3. Prepreg honeycomb material; 4. Processed surface; 5. Molded surface. Detailed Implementation

[0025] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0026] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be located directly on or indirectly on the other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to the other component.

[0027] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate that the device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0028] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating relative importance or the number of technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. The specific implementation of this invention will be described in more detail below with reference to specific embodiments: This embodiment takes the manufacturing of a certain type of hyperboloid aramid paper honeycomb core material as an example to explain in detail the implementation process of this method. The upper surface (skin bonding surface) of the honeycomb core material is a complex hyperboloid, requiring that the direction of the honeycomb cell grid and the direction of the cell wall be strictly perpendicular to the surface; the lower surface (inner side) is also a complex hyperboloid.

[0029] Step S1: Analysis and determination of the forming surface and the machining surface.

[0030] Based on the 3D digital model analysis of the product, the upper curved surface is the main aerodynamic bearing surface, and has strict requirements on the direction of the honeycomb grid and the direction of the grid walls; therefore, it is determined as the forming surface. The lower curved surface is correspondingly determined as the machining surface.

[0031] Step S2: Design and manufacture of detachable molds.

[0032] Based on the digital model of the molding surface, a combination mold is designed. The base layer 1 is made of spliced ​​aluminum alloy frame with internal reinforcing ribs to ensure overall rigidity.

[0033] The removable layer 2 is made of 2mm thick fiberglass (epoxy resin-based glass fiber composite material) and manufactured by CNC machining. Its working surface is a precise negative of the forming surface, and the surface accuracy needs to reach ±0.1mm. Multiple positioning holes are machined at the edges and key locations of the removable layer 2.

[0034] Positioning holes of the same precision and size are machined at corresponding positions on base layer 1. High-precision positioning pins are used to precisely fix the detachable layer 2 onto base layer 1, together forming the molding die.

[0035] Step S3: Cellular curing and molding.

[0036] Material preparation calculation: From the offset of the forming surface to the complete envelopment of the processing surface, the minimum distance n is measured to be 22mm. A 4mm processing allowance is reserved, therefore, aramid paper honeycomb with a thickness of m=22+4=26mm and pre-impregnated with epoxy resin is selected as the blank.

[0037] Laying and Encapsulation: The pre-prepared honeycomb blank (slightly larger than the projected surface of removable layer 2) is laid on the surface of removable layer 2. Then, a porous breathable membrane and an air-guiding felt are laid in sequence, covered with a vacuum bag film and sealed to form a pre-formed component.

[0038] Curing: The entire preformed assembly is pushed into an autoclave. The curing process is executed, and after curing, it is cooled in the oven to below 60°C before being removed. At this point, the lower surface of the honeycomb has been precisely shaped into the desired curved surface.

[0039] Step S4: CNC machining.

[0040] Clamping: Remove the component from the autoclave and remove the vacuum bag material. Remove the removable layer 2 with the cured honeycomb (still connected to the base layer 1) entirely from the base layer 1. Then, precisely install the removable layer 2 onto the worktable of the five-axis CNC machine tool through its positioning holes using a special fixture.

[0041] Machining: The machining program for the machined surface is called in the CNC system. A dedicated honeycomb milling cutter (such as a pineapple end mill) is used, and a high-speed milling process is employed to finish the upper surface of the honeycomb. During machining, air cooling is used to avoid dust pollution. After machining, the upper surface of the honeycomb (machined surface 4) achieves the precise curved surface required by the drawing.

[0042] Step S5: Overall transfer and adhesive positioning.

[0043] After processing and cleaning, there is no need to peel the honeycomb from the removable layer 2. The entire component, formed by combining the honeycomb with the removable layer, is precisely installed onto the subsequent bonding mold using positioning pins through the uniform positioning holes on the removable layer 2. This bonding mold has a matching positioning structure. Subsequently, subsequent processes such as skin application, co-curing, or secondary bonding can be performed in this state, ensuring the precise positioning of the honeycomb core material is maintained.

[0044] In summary, this invention systematically solves the precision, performance, and process challenges in the manufacturing of hyperboloid honeycomb through innovative mold design and process flow, and has high engineering application value.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-precision molding and processing method for hyperboloid honeycomb, characterized in that, Includes the following steps: S1. According to the technical requirements of hyperboloid honeycomb, the curved surface that needs to be perpendicular to the direction of the honeycomb cell grid and the direction of the cell grid wall is determined as the forming surface, and the other surface is determined as the processing surface. S2. Design and manufacture a mold according to the shape of the forming surface. The mold includes a base layer, a detachable layer and a positioning structure. The detachable layer is fitted with the forming surface, and the positioning structure connects the detachable layer and the base layer. S3. The prepreg honeycomb material is laid and fixed on the surface of the removable layer to form a preformed component, so that the lower surface of the prepreg honeycomb material is completely in contact with the surface of the removable layer, and the direction of the honeycomb pores and the direction of the pore walls are consistent with the normal direction of the forming surface. The preformed component is vacuum-sealed and then cured. S4. After curing, the removable layer with the cured honeycomb is fixed as a whole on a CNC machine tool, and the honeycomb processing surface is CNC machined to obtain the hyperboloid honeycomb with the final designed shape. S5. Separate the processed hyperboloid honeycomb along with the detachable layer from the base layer, and position the detachable layer and the hyperboloid honeycomb as a whole through the positioning structure and transfer them to the bonding mold for subsequent bonding processes.

2. The high-precision forming and processing method for hyperboloid honeycomb as described in claim 1, characterized in that, In step S2, the removable layer is made of a composite material with a thickness of 0.5 mm to 3 mm.

3. The high-precision forming and processing method for hyperboloid honeycomb as described in claim 2, characterized in that, The composite material is fiberglass or carbon fiber laminate.

4. The high-precision forming and processing method for hyperboloid honeycomb as described in claim 1, characterized in that, The positioning structure is a positioning hole provided on the removable layer and the base layer, or a positioning hole provided on the removable layer and the bonding mold.

5. The high-precision forming and processing method for hyperboloid honeycomb as described in claim 1, characterized in that, In step S3, the pre-impregnated honeycomb material is a honeycomb of uniform thickness, and its thickness m satisfies the formula: m=n+(3~5) mm, where n is the distance offset from the molding surface to the point that can completely enclose the processing surface.

6. The high-precision forming and processing method for hyperboloid honeycomb as described in claim 5, characterized in that, In step S3, the curing process includes: laying auxiliary materials on a mold on which pre-impregnated honeycomb material has been laid to complete vacuum sealing, forming a pre-formed component with the mold, and then placing the pre-formed component into a vacuum chamber for heating and curing.

7. The high-precision forming and processing method for hyperboloid honeycomb as described in claim 1, characterized in that, The preimpregnated honeycomb material is one of aramid paper honeycomb, glass cloth honeycomb, or aluminum honeycomb, and its preimpregnated resin is an epoxy resin-phenolic resin system.

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