Metal-to-composite joint structure and method of forming same

Abstract

This invention belongs to the field of metal and composite material joining and forming, specifically relating to a metal and composite material joining structure and its forming method. The metal and composite material joining structure includes: an inner support member, a composite material layer, and a metal inlay. The metal inlay is a hollow double-forked structure with an annular positioning platform on its inner wall. The small end of the inner support member is bonded to the inner wall of the metal inlay. The connection between the large and small ends of the inner support member is axially positioned via the end face of the metal inlay. The inner support member and the metal inlay are covered with a composite material layer. The outer surface of the metal inlay features, in sequence, a large cylindrical segment, a small cylindrical segment, and a double-forked lug. There is a smooth, equal-angle transition between the large and small cylindrical segments and between the small cylindrical segment and the double-forked lug, with a transition angle between 4-15°. The outer surface of the large cylindrical segment has a cylindrical groove with a groove depth ≥2.0 mm.

Description

Technical Field

[0001] This invention belongs to the field of metal and composite material connection and forming, and specifically relates to a metal and composite material connection structure and its forming method. Background Technology

[0002] Helicopter control sticks and rotor pitch control sticks are core components of helicopters. To achieve lightweight design, composite material control sticks are used. Traditional metal-to-composite material connections use adhesive bonding, riveting, and bolting. Adhesive bonding suffers from aging over time and in humid and hot environments, leading to decreased connection strength. Riveting and bolting disrupt the continuity of the composite matrix, causing initial defects, stress concentration, and further reducing connection strength. Because helicopter control systems operate under unique high-cycle fatigue loads and are critical components of the rotor system, failure of these systems can cause control failure and severe catastrophic events. Traditional adhesive bonding, riveting, and bolting cannot meet the lifespan, reliability, and lightweight requirements of helicopters under high-cycle fatigue conditions. Summary of the Invention

[0003] Purpose of the invention: This invention provides a metal-composite material connection structure and its forming method, which improves the life and reliability of helicopters under high-cycle fatigue while meeting lightweight requirements.

[0004] Technical solution: A metal-composite material connection structure includes: an inner support, a composite material layer, and a metal inlay. The metal inlay is a hollow double-forked structure with an annular positioning platform on its inner wall. The small end of the inner support is bonded to the inner wall of the metal inlay. The connection between the large and small ends of the inner support is axially positioned through the end face of the metal inlay. The inner support and the metal inlay are covered with a composite material layer. The outer surface of the metal inlay features, in sequence, a large cylindrical segment, a small cylindrical segment, and a double-forked lug. The transition between the large and small cylindrical segments and between the small cylindrical segment and the double-forked lug is smooth and at equal angles, with the transition angle between 4-15°. The outer surface of the large cylindrical segment has a cylindrical groove with a groove depth ≥2.0 mm.

[0005] Furthermore, it also includes: a shoulder bushing fixed to the double-fork lug structure by a hole extrusion process.

[0006] Furthermore, the internal support component is made of carbon fiber composite material.

[0007] Furthermore, the interference fit between the shoulder bushing and the fork lug in the diameter direction is >0.6mm.

[0008] Furthermore, the minimum thickness of the metal connector for the metal insert is ≥3.0mm.

[0009] Furthermore, the surface roughness Ra of the large cylindrical section, the small cylindrical section, and the transition section is ≥10.

[0010] A method for forming the above-mentioned metal-composite material connection structure includes: Step 1: Apply R-230 structural adhesive to the mating surfaces of the metal insert and the inner support. Step 2: Install the inner support and metal inserts onto the mold, and then allow the structural adhesive to cure after axial positioning through the double-forked lug structure holes of the metal inserts. Step 3: Apply a layer of adhesive film to the outer surface of the metal inlay and the outer surface of the support, with the adhesive film overlapping by 1-3mm. Step 4: The outer surface of the metal inlay and the outer surface of the inner support are wrapped with trapezoidal fabric. After the long protrusion of the trapezoidal fabric wraps and fills the groove area of ​​the metal inlay, the groove area should be 0.1-0.5mm higher than the outer cylindrical surface. Then wrap the whole thing. After wrapping, wrap and compact it with BOPP tape. Then use tooling to compact the outer surface of the metal inlay. Wrap and compact it with BOPP tape. Specifically, the tension of the BOPP tape is ≥40N and the tape spacing is ≤5mm. After wrapping the BOPP tape, leave it for at least 30 minutes to compact it. After compaction, remove the BOPP tape. Step 5: Place the connection structure and tooling in a curing oven for the first curing: Step 6: After the first curing, sand the cured outer surface with sandpaper and apply J-81 structural adhesive; Step 7: Apply release cloth to the fork lug area of ​​the metal insert for protection; Step 8: Wrap with M40J carbon fiber bundles at a 10° angle, with the proportion of 10° angle wrapping not less than 70%, and then fill the wrapped area with M40J carbon fiber bundles. Step 9: Press the metal insert area firmly with a tool; Step 10: Place in a vacuum bag and vacuum-seal; Step 11: Place the vacuum-sealed connection structure into the curing oven for a second curing; the maximum temperature of the second curing is lower than the maximum temperature of the first curing.

[0011] Furthermore, the total length L1 of the trapezoidal covering is greater than twice the total length of the metal inlays; The maximum length L2 of the groove area corresponding to the trapezoidal fabric covering is 10-30mm. The width H1 of the trapezoidal wrapping fabric can be wrapped around the metal connector insert in more than 3 layers, and the width H2 of the long boss ensures that the outer contour is 0.1-0.5mm higher than the outer cylindrical surface after wrapping.

[0012] Furthermore, the curve for the first curing stage is as follows: .

[0013] Furthermore, the curve for the second curing is as follows: .

[0014] Beneficial effects: (1) The metal-composite connection method of this application has the characteristics of long service life, high reliability and light weight; (2) The molding process of this application is reliable and can prevent the inserts from detaching, thus ensuring safety; (3) Dual-path transmission ensures safety; (4) The connection structure of this application has passed the high-cycle fatigue test. Under the action of 10000±35831.8N, the ear hole of the metal insert is broken, but the connection between the composite material and the metal is not damaged, indicating that it has a good connection effect.

[0015] (5) The connection form and molding method of this application are not only applicable to rotor systems, but also to structures such as helicopter control structures and composite material support rods for fixed-wing aircraft. Attached Figure Description

[0016] 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.

[0017] Figure 1 This is an isometric view of the connection structure according to an embodiment of this application; Figure 2 This is a cross-sectional view of the connection structure according to an embodiment of this application; Figure 3 An isometric view of a metal inlay according to an embodiment of this application; Figure 4 This is a cross-sectional view of a metal inlay according to an embodiment of this application: the dashed ear area is the protective area when the carbon fiber is wound; Figure 5 This is a schematic diagram of the composite layer layup of the connection structure according to an embodiment of this application; Figure 6 This is a schematic diagram of a trapezoidal fabric covering. Figure 7 This is a schematic diagram of the tooling; Among them, 1. Inner support; 2. Composite material layer; 3. Metal inlay; 4. Shoulder bushing; 21. Trapezoidal fabric wrapping layer; 22. Carbon fiber bundle wrapping layer; 23. Wrapping filling area. Detailed Implementation

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] This invention proposes a highly reliable metal-composite connection structure and an adapted forming process, which has been verified under high cycle fatigue conditions, exhibiting excellent performance and enabling long life and lightweight design.

[0025] This invention provides a metal-composite material connection structure. This metal insert-composite material connection structure features high reliability, long lifespan, and high safety. The connection structure employs both mechanical and adhesive bonding for load transfer. Electron beam texturing technology is used at the interface to improve surface roughness, thereby enhancing the strength of the adhesive bond. The mechanical connection is achieved through conical and grooved surfaces. After co-curing, the connection between the composite material and the metal insert is a conical surface and a groove, allowing load transfer through the compressive force between the metal and the composite material. To ensure the reliability of the mechanical connection, a trapezoidal fabric covering process is used. The trapezoidal covering is a satin-textured fabric with equivalent mechanical properties in both the warp and weft directions. The warp direction can transfer axial loads, while the weft direction ensures that the warp carbon fibers remain tight and do not loosen during axial load transfer, guaranteeing a strong connection between the metal insert and the composite material and ensuring safety. Strength calculations show that both adhesive bonding and mechanical connection can effectively transfer control loads, providing double protection. Even if the adhesive bonding fails, the load will still be transferred through the mechanical connection. This connection method ensures that the metal insert does not detach, guaranteeing flight test safety.

[0026] like Figure 1-7 A metal and composite material connection structure includes: an inner support 1, a composite material layer 2, a metal inlay 3, and a shoulder bushing 4.

[0027] The metal inlay 3 has a double-fork lug structure. The fork lugs are tightly fitted with the shoulder bushing 4 to protect the metal inlay body. The double-fork lug structure is connected to other external parts.

[0028] The end face of the inner support 1 contacts the metal insert 3 for axial positioning. Considering weight reduction and connection strength, the material of the inner support is carbon fiber composite material.

[0029] For the metal insert 3, the fork lug and the shoulder bushing 4, the hole extrusion process is preferred. The interference fit between the shoulder bushing 4 and the fork lug in the diameter direction is >0.6mm to improve the fatigue performance of the connecting hole. In addition to the hole extrusion process, interference fit assembly can also be used.

[0030] The outer surface features of the metal inlay 3 are, in sequence, a large cylindrical section, a small cylindrical section, and a double-forked lug; the transition between the large cylindrical section and the small cylindrical section, and between the small cylindrical section and the double-forked lug, is smooth and at equal angles, with the transition angle between 4 and 15°.

[0031] The outer surface of the large cylindrical section has a cylindrical groove. To ensure the compressive strength of the connecting metal and composite material, the groove depth is ≥2.0mm, while ensuring the maximum compressive strength (maximum load / compression area) is ≤300MPa. The interior has a large cylindrical groove with steps for installation positioning. To ensure the strength of the connection, the minimum thickness of the metal insert 3 is ≥3.0mm.

[0032] The small cylindrical section has a through groove, which is used to reduce weight and also to install the mold during curing.

[0033] The small cylindrical section and the double-forked lug section have large grooves to reduce weight.

[0034] The outer surfaces of the large cylindrical section, the small cylindrical section, and the transition section are roughened to increase surface roughness, with a roughness Ra≥10, thereby improving the connection strength between the metal and the composite material.

[0035] The preferred materials for the metal insert 3 are titanium alloy and stainless steel, which can prevent electrochemical corrosion at the connection with the composite material. If structural steel must be used, a layer of glass cloth must be laid on the surface of the structural steel for electrochemical corrosion protection.

[0036] Molding process scheme for metal insert 3 and composite material: (1) Apply sufficient release agent to the mold surface, apply appropriate amount of release agent to the surface of the inner hole of the metal insert that mates with the mold; apply R-230 structural adhesive to the mating part of the metal insert 3 and the inner support 1. (2) Install the inner support 1 and the metal insert 3 on the mold, and achieve axial positioning through the double fork hole of the metal joint. After positioning, let it stand for 24 hours at (25±5)℃ to allow the structural adhesive to cure. (3) A layer of adhesive film is laid on the outer surface of the metal inlay 3 and the outer surface of the support 1. The adhesive film overlaps, and the overlap length is 1-3mm. (4) The metal and composite materials are wrapped with trapezoidal wrapping cloth to form a trapezoidal wrapping cloth layer 21; the long boss first wraps the groove area of ​​the metal inlay, wraps and compacts it. After wrapping, the groove area should be 0.1-0.5mm higher than the outer cylindrical surface. Then wrap the whole thing. After the wrapping is completed, wrap and compact it with BOPP tape. The tension of BOPP tape is ≥40N and the tape spacing is ≤5mm. After the BOPP tape is wrapped, place it for at least 30 minutes to compact it. After compaction, remove the BOPP tape and use tooling to compact the outer surface of the metal inlay.

[0037] (5) Principles for determining the dimensions of the trapezoidal wrapping: L1: the total length of the composite layer. To ensure the strength of the connection, the length of L1 should be greater than twice the total length of the metal inlay; L2: the maximum length of the groove area, L2 length is 10-30mm; L3: the minimum length of the groove area, slightly less than the length of L2; H1 width can wrap around the metal joint inlay more than 3 times, that is, 3 times the circumference of the cylinder; H2 length is related to the groove depth, ensuring that the outer contour of the H2 area is slightly higher than the end face of the metal joint after wrapping. (6) Place the structural components and tooling in a curing oven for the first curing. The first curing curve is as follows:

[0038] (7) After the first curing, sand the first cured outer surface with sandpaper and apply J-81 structural adhesive; (8) Apply release cloth to the fork lug area of ​​the metal insert for protection; (9) Wrapping composite material layers; a) Two bundles of M40J carbon fiber are wound to form a carbon fiber winding layer 22 with a yarn width of 3.5mm. To ensure axial mechanical properties, the winding is done at a small angle, and the proportion of winding angles less than 10 degrees is not less than 70%. In this example, the winding angles are ±104° / 90° / ±104° / 90° / ±104° / 90° / ±104° / 90° (±10° is repeated 4 times, 90° is repeated once, ±10° is repeated 4 times, 90° is repeated once, ±10° is repeated 4 times, 90° is repeated once, ±10° is repeated 4 times, 90° is repeated once, ±10° is repeated 4 times, 90° is repeated three times); at the same time, the winding filling area 23 is filled with M40J carbon fiber bundles. b) Measure the actual outer diameter after each winding cycle; c) If a yarn breaks during winding, remove that layer, connect the yarn in a non-product area, and then rewind. d) After all the carbon fiber wrapping is completed, lay a layer of glass cloth on the outermost layer for protection; e) Trim away the carbon fiber at the end cap and any excess carbon fiber; (10) Use a tooling to compact the metal inlay area to ensure it fits firmly; the tooling consists of two halves, which are tightened with bolts.

[0039] (11) The structural components and joint fixtures are placed together in a vacuum bag and vacuumed; (12) Second curing: Place the vacuum-evacuated structural component into a curing oven for curing. The curing curve is as follows:

[0040] To ensure that the second curing does not affect the effect of the first curing, the maximum temperature of the second curing is lower than the maximum temperature of the first curing.

[0041] (13) After the second curing, grind the outer surface and check the appearance quality.

[0042] The key to the molding scheme of this invention is ensuring the strength of the connection between the metal insert and the composite material: the trapezoidal wrapping is the key and core, and the length of the trapezoidal wrapping and the length of the long boss are designed. After wrapping, BOPP tape is compacted, and after compaction, a first curing is performed to ensure the reliability of the connection. At the same time, in order to ensure axial mechanical properties, the wrapping angle is a small angle, and the proportion of wrapping angles less than 10 degrees is not less than 70%.

[0043] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A metal-composite material connection structure, characterized in that, include: The device comprises an inner support component, a composite material layer, and a metal inlay. The metal inlay is a hollow double-forked structure with an annular positioning platform on its inner wall. The small end of the inner support component is bonded to the inner wall of the metal inlay. The connection between the large and small ends of the inner support component is axially positioned through the end face of the metal inlay. The inner support component and the metal inlay are covered with a composite material layer. The outer surface of the metal inlay features a large cylindrical section, a small cylindrical section, and a double-forked lug in sequence. The transition between the large and small cylindrical sections and between the small cylindrical section and the double-forked lug is smooth and at equal angles, with the transition angle between 4-15°. The outer surface of the large cylindrical section has a cylindrical groove with a groove depth ≥2.0mm.

2. The metal-composite material connection structure according to claim 1, characterized in that, Also includes: Shoulder bushings fixed to the double-fork lug structure by a hole extrusion process.

3. The metal-composite material connection structure according to claim 1, characterized in that, The internal support component is made of carbon fiber composite material.

4. The metal-composite material connection structure according to claim 2, characterized in that, The interference fit between the shoulder bushing and the fork lug in the diameter direction is >0.6mm.

5. The metal-composite material connection structure according to claim 1, characterized in that, The minimum thickness of the metal insert and metal connector is ≥3.0mm.

6. The metal-composite material connection structure according to claim 4, characterized in that, The surface roughness Ra of the large cylindrical section, the small cylindrical section, and the transition section is ≥10.

7. A molding method for a metal-composite material connection structure as described in any one of claims 1-6, characterized in that, include: Step 1: Apply R-230 structural adhesive to the mating surfaces of the metal insert and the inner support. Step 2: Install the inner support and metal inserts onto the mold, and then allow the structural adhesive to cure after axial positioning through the double-forked lug structure holes of the metal inserts. Step 3: Apply a layer of adhesive film to the outer surface of the metal inlay and the outer surface of the support, with the adhesive film overlapping by 1-3mm. Step 4: The outer surface of the metal inlay and the outer surface of the inner support are wrapped with trapezoidal fabric. After the long protrusion of the trapezoidal fabric wraps and fills the groove area of ​​the metal inlay, the groove area should be 0.1-0.5mm higher than the outer cylindrical surface. Then wrap the whole thing. After wrapping, wrap and compact it with BOPP tape. Then use tooling to compact the outer surface of the metal inlay. Wrap and compact it with BOPP tape. Specifically, the tension of the BOPP tape is ≥40N and the tape spacing is ≤5mm. After wrapping the BOPP tape, leave it for at least 30 minutes to compact it. After compaction, remove the BOPP tape. Step 5: Place the connection structure and tooling in a curing oven for the first curing: Step 6: After the first curing, sand the cured outer surface with sandpaper and apply J-81 structural adhesive; Step 7: Apply release cloth to the fork lug area of ​​the metal insert for protection; Step 8: Wrap with M40J carbon fiber bundles at a 10° angle, with the proportion of 10° angle wrapping not less than 70%, and then fill the wrapped area with M40J carbon fiber bundles. Step 9: Press the metal insert area firmly with a tool; Step 10: Place in a vacuum bag and vacuum-seal; Step 11: Place the vacuum-sealed connection structure into the curing oven for a second curing; the maximum temperature of the second curing is lower than the maximum temperature of the first curing.

8. The method according to claim 7, characterized in that, The total length L1 of the trapezoidal fabric covering is greater than twice the total length of the metal inlays; The maximum length L2 of the groove area corresponding to the trapezoidal fabric covering is 10-30mm. The width H1 of the trapezoidal wrapping fabric can be wrapped around the metal connector insert in more than 3 layers, and the width H2 of the long boss ensures that the outer contour is 0.1-0.5mm higher than the outer cylindrical surface after wrapping.

9. The method according to claim 7, characterized in that, The curve for the first curing stage is as follows: 。 10. The method according to claim 7, characterized in that, The curve for the second curing is as follows: 。

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