A method for treating a lightning protection connection area of a composite material structure

Abstract

A method for treating a lightning protection connection area of a composite material structure provided by the present application, the method comprising: grinding a copper mesh in a lightning protection connection area of an epoxy resin-based composite material structure; spraying a conductive metal layer on the copper mesh; wherein, the conductive metal layer includes a gradient transition layer and a metal surface layer; in the present application, a copper mesh is ground in a lightning protection connection area of a composite material structure, a conductive metal layer with a certain thickness is sprayed on the exposed copper mesh area through an explosion spraying process, and then connected to an internal metal through a fastener with good electrical conductivity to form a lightning protection lap path, having good lightning protection performance.

Description

Technical Field

[0001] This application belongs to the technical field of helicopter structure design, and particularly relates to a method for treating a lightning protection connection area of a composite material structure. Background Technique

[0002] The composite material structure of an aircraft is mainly composed of fibers (carbon fiber, graphite fiber, glass cloth or Kevlar) and resin. These two materials usually have poorer electrical conductivity than metals and can basically not disperse and conduct electric current, especially lightning current. The most effective way to solve the lightning protection of composite materials is to metallize the surface of the composite materials.

[0003] There are three common methods for metallizing the surface of composite materials:

[0004] One is to apply a metal layer on the surface. The metal foil is connected to the substrate through an adhesive or a metal layer such as zinc, aluminum, copper, etc. with a certain thickness is prepared on the surface of the substrate by means of arc spraying, flame spraying, etc. The surface coating method has good effects on both electromagnetic shielding and conductivity. However, due to certain deficiencies in the bonding force between the metal layer and the substrate and the preparation process, the weight cost is high and the application is subject to certain limitations.

[0005] The second is to coat conductive paint. Metal-based conductive paint has good electrical conductivity and excellent shielding performance. It is one of the varieties that have been developed earlier and applied more. However, when applied in the fields of aviation and aerospace, there are still disadvantages such as high areal density, poor flexibility, and low adhesion.

[0006] The third is to use a metal mesh. As a conductive, lightning protection and electromagnetic shielding layer, it is one of the most preferred solutions in foreign aircraft design and is also the main method for lightning protection design of the composite material structure of current helicopters. Compared with the first two types of products, it has a relatively light weight, and there is no disadvantage that the conductive filler in the conductive paint is easy to precipitate. At the same time, it can avoid the conductivity fluctuation caused by the difference in the dispersion state of the conductive filler after the conductive paint is cured; when used as a structure for lightning protection design, it needs to be connected to the internal metal frame beam through conductive fasteners (rivets, bolts, etc.).

[0007] The structures metallized by the first two methods can be directly connected. For the structure using a metal mesh (mainly a copper mesh), the current common method is to polish the connection area to expose the copper mesh and use conductive glue to bond copper strips. The resistivity of the conductive glue is 1 - 2×10-6 Ω·m, which is much larger than 1.7×10-8 Ω·m of copper. The local increase in resistance will affect the transmission of current during lightning to a certain extent, and there is a risk of delamination during long-term use of the bonding;

[0008] Therefore, a method for treating a lightning protection connection area of a composite material structure provided by this application can effectively solve this problem. Summary of the Invention

[0009] In view of the above technical problems, the present application provides a method for treating a lightning protection connection area of a composite material structure, the method comprising:

[0010] Grind out a copper mesh in the lightning protection connection area of the epoxy resin-based composite material structure;

[0011] Spray a conductive metal layer on the copper mesh; wherein, the conductive metal layer includes a gradient transition layer and a metal surface layer.

[0012] Preferably, before grinding out the copper mesh in the lightning protection connection area of the epoxy resin-based composite material structure, it further includes:

[0013] Manufacture an epoxy resin-based composite material structure; wherein, a copper mesh and a glass cloth are laid on the outer surface of the epoxy resin-based composite material structure.

[0014] Preferably, grinding out the copper mesh in the lightning protection connection area of the epoxy resin-based composite material structure includes:

[0015] Use 200-mesh sandpaper to grind the glass cloth and resin covering the outside of the copper mesh;

[0016] Continue to grind the surface with 400-mesh sandpaper until the copper mesh is exposed, clean the surface with acetone, and keep the surface dry.

[0017] Preferably, before using 200-mesh sandpaper to grind the glass cloth and resin covering the outside of the copper mesh, it further includes:

[0018] On the outer surface of the manufactured composite material structure part in the area where lap conduction is required, use a pencil to mark the boundary and stick tape on the outside for protection.

[0019] Preferably, spraying the conductive metal layer on the copper mesh includes:

[0020] Adopt an explosive spraying method to spray and form a gradient transition layer on the copper mesh;

[0021] Adopt an explosive spraying method to spray and form a metal surface layer on the gradient transition layer.

[0022] Preferably, the material of the gradient transition layer is low-melting-point metal aluminum, the aluminum powder is used in the explosive spraying, and the particle size range of the aluminum powder is 10-45μm.

[0023] Preferably, the material of the metal surface layer is copper with excellent conductivity, spherical copper powder is used in the explosive spraying, and the particle size range of the spherical copper powder is 15-45μm.

[0024] Preferably, the tensile bonding strength value of the coating by explosive spraying is greater than 6.5MPa, the coating porosity is less than 1.5%; the coating resistance is of the same order of magnitude as that of a copper foil with the same thickness.

[0025] Advantageous technical effects of the present application:

[0026] In the present application, a copper mesh is ground in the lightning protection connection area of the composite material structure. A conductive metal layer with a certain thickness is sprayed in the exposed copper mesh area by an explosion spraying process, and then connected to the internal metal through fasteners with good electrical conductivity to form a lightning protection lap path, having good lightning protection performance. Description of the Drawings

[0027] Figure 1 It is a schematic diagram of the lightning protection edge structure provided by an embodiment of the present application. Detailed Embodiments

[0028] In an embodiment of the present application, a copper mesh is ground in the lightning protection connection area of the composite material structure. A conductive metal layer with a certain thickness is sprayed in the exposed copper mesh area by an explosion spraying process, and then connected to the internal metal through fasteners with good electrical conductivity to form a lightning protection lap path. For epoxy resin-based composite materials, the conductive metal layer is designed with a two-layer structure of a gradient transition layer and a metal surface layer ( Figure 1 ), where the gradient transition layer is low-melting-point metal Al and the surface layer material is Cu material with excellent electrical conductivity. Specifically:

[0029] Among them, an epoxy resin-based composite material laminated structure or honeycomb sandwich structure is manufactured according to the structural design drawings, and a lightning protection integrated adhesive film or a copper mesh plus fiberglass cloth protection suitable for the lightning protection zone where the structure is located is laid on the outer surface, and the part dimensions are processed to the final state without leaving any allowance.

[0030] Furthermore, on the outer surface of the manufactured composite material structure parts in the areas where lap conduction is required, the boundaries are marked with a pencil, and tape is pasted on the outside for protection. First, the fiberglass cloth and resin covering the copper mesh are ground with 200-mesh sandpaper, and then the surface is continuously ground with 400-mesh sandpaper until the copper mesh is exposed. After cleaning the surface with acetone, keep the surface dry.

[0031] It should be noted that the traditional process methods for spraying metal coatings on resin-based composite materials are plasma spraying and flame spraying. Plasma spraying and flame spraying are continuous thermal spraying, and the heat input during the spraying process is relatively large. The resin-based composite material itself has very poor thermal conductivity, and generally, a coating needs to be prepared by intermittent spraying and pre-curing metal powder on the composite material; at the same time, the coating porosity and oxide content are relatively high, and the bonding strength is relatively low. For example, the lowest porosity of the flame spraying coating is 7.61%, and the highest bonding strength is 2.3 MPa.

[0032] In other embodiments of the present application, the method of using explosion spraying technology to prepare a metal coating on the surface of resin-based composite materials has the following advantages:

[0033] First, explosive spraying is a pulsed spraying method. By controlling the pulse frequency and process parameters, the effective adjustment of the heat input can be achieved, thereby reducing the risk of thermal damage to the substrate material during the spraying process.

[0034] Secondly, the high-speed shock wave can quickly heat and accelerate the spraying particles. With the assistance of reducing gases, the density and bonding strength of the coating can be significantly improved, and the oxide content inside the coating can be reduced.

[0035] Among them, to reduce the damage to the composite material structure, aluminum with a lower melting point is first sprayed as the gradient layer, and then the surface copper layer is sprayed. The aluminum powder used in explosive spraying has a particle size range of 10 - 45μm; the spherical copper powder has a particle size range of 15 - 45μm.

[0036] In a feasible implementation manner, the main spraying parameters that need to be controlled during the spraying process include: gun frequency, oxygen-fuel ratio, spraying distance, powder feeding amount, and distance, etc. The main process parameters adopted during the spraying process of the present invention are shown in the following table:

[0037]

[0038] Among them, the tensile bonding strength value of the explosive spraying coating is greater than 6.5MPa, the coating porosity is less than 1.5%, and the coating resistance is of the same order of magnitude as that of the copper foil with the same thickness;

[0039] Finally, it should be noted that to verify the technical effect of the lightning protection connection area prepared according to this application, test pieces are prepared by using the current conventional method, that is, conductive adhesive plus copper bars, and test pieces are prepared according to the treatment method provided by this application. Current injection tests are respectively carried out in lightning strike zone 2A. After the lightning strike, the state of the test pieces is as follows: disassemble the rivets in the connection area, observe the damage situation at the hole edge under an electron microscope, and the damage situation of the connection holes of the test pieces prepared by the conventional method is obvious.

[0040] For the test pieces prepared by the method provided by this application, the damage situation of the connection holes is almost none, indicating that this application can effectively improve the lightning protection effect of the lightning protection connection area of the composite material structure.

Claims

1. A method for treating a lightning protection connection area of a composite material structure, characterized in that, The method includes: Grinding out a copper mesh in the lightning protection connection area of the epoxy resin-based composite material structure; Spraying a conductive metal layer on the copper mesh; wherein, the conductive metal layer includes a gradient transition layer and a metal surface layer; the coating resistance is of the same order of magnitude as that of a copper foil with the same thickness.

2. The method according to claim 1, characterized in that, Before grinding out the copper mesh in the lightning protection connection area of the epoxy resin-based composite material structure, it further includes: Manufacturing an epoxy resin-based composite material structure; wherein, a copper mesh and a fiberglass cloth are laid on the outer surface of the epoxy resin-based composite material structure.

3. The method according to claim 2, wherein Grinding out the copper mesh in the lightning protection connection area of the epoxy resin-based composite material structure includes: Grinding the fiberglass cloth and resin covering the copper mesh with 200-mesh sandpaper; Continuing to grind the surface with 400-mesh sandpaper until the copper mesh is exposed, cleaning the surface with acetone, and keeping the surface dry.

4. The method according to claim 3, characterized in that, Before grinding the fiberglass cloth and resin covering the copper mesh with 200-mesh sandpaper, it further includes: On the outer surface of the manufactured composite material structure part, marking the boundary with a pencil in the area where lap conduction is required, and pasting a tape on the outside for protection.

5. The method according to claim 1, wherein Spraying the conductive metal layer on the copper mesh includes: Spraying to form a gradient transition layer on the copper mesh by using an explosive spraying method; Spraying to form a metal surface layer on the gradient transition layer by using an explosive spraying method.

6. The method according to claim 5, wherein The material of the gradient transition layer is low-melting-point metal aluminum, the aluminum powder is used in the explosive spraying, and the particle size range of the aluminum powder is 10 - 45 μm.

7. The method according to claim 5, wherein The material of the metal surface layer is copper with excellent conductivity, the spherical copper powder is used in the explosive spraying, and the particle size range of the spherical copper powder is 15 - 45 μm.

8. The method according to claim 5, wherein The tensile bonding strength value of the coating by the explosive spraying is greater than 6.5 MPa, and the coating porosity is less than 1.5%.

Images