Integrated variable-pitch pull rod and forming method thereof

Abstract

The invention belongs to the technical field of helicopter automatic inclinator variable pitch pull rod structure design, and particularly relates to an integrated variable pitch pull rod and a forming method thereof. The variable-pitch pull rod comprises two composite material joints (1), a composite material pull rod body (2) and four shoulder bushings (3), wherein inward bosses are formed at the joints of the large inner diameter sections and the small inner diameter ends of the composite material joints (1); the outer circle of the composite material connector (1) is in an inverted cone shape. The outer diameter of the end part of the composite material pull rod body inner pipe (2.1) is smaller than that of the middle section; the inner circles at the two ends of the composite material pull rod body outer pipe (2.2) are inverted cone-shaped; an annular positioning boss is arranged on the end face of the shoulder bush (3), and a linear positioning boss is arranged in the axial direction of the shoulder bush (3). The four convex shoulder bushings (3) are respectively pre-buried in lug holes of the double insertion lugs of the composite material joint (1); the two composite material joints (1) are respectively formed at two ends of the composite material pull rod body (2).

Description

Technical Field

[0001] The invention belongs to the technical field of variable pitch pull rod structure design of helicopter automatic tilt device, and in particular relates to an integrated variable pitch pull rod and a forming method thereof. Background Art

[0002] Traditional helicopter automatic tilt devices use metal rods to achieve pitch-changing motion. In comparison, the stiffness of aluminum alloy rods does not meet the design requirements, and stainless steel rods are heavy. In order to achieve the goal of weight reduction while still ensuring the design strength, stiffness, and stability requirements, composite rods have become the first choice for helicopter pitch-changing rod weight reduction design. Currently, most composite rods on the market are in the form of metal joints + composite rods, and the composite materials and metal materials are connected by bonding. However, the bonding performance of composites and metals is difficult to control, and failures such as metal shank joint bearing fractures, composite / metal connection failures, and composite interlayer failures occur from time to time. Most of the reasons are attributed to poor molding processes and defects in the structural design of metal joints. Summary of the invention

[0003] Purpose of the invention: To provide an integrated variable pitch tie rod and a forming method thereof, so as to avoid the problems of unstable bonding performance between metal joints and composite materials and low strength of threaded connection between shank spherical bearings and metal joints.

[0004] Technical solution:

[0005] An integrated variable pitch tie rod comprises: two composite material joints 1, a composite material tie rod body 2, and four shoulder bushings 3, wherein the composite material joint 1 is made of T700, is axially hollow, and comprises a large inner diameter section, a small inner diameter section, and double plug ears from the inside to the outside, wherein an inward boss is formed at the connection between the large inner diameter section and the small inner diameter end; the outer circle of the composite material joint 1 is an inverted cone; the composite material tie rod body 2 is made of CCM55J, and the composite material tie rod body 2 comprises a composite material tie rod inner tube 2.1 and a composite material tie rod outer tube 2.2, wherein the outer diameter of the end of the composite material tie rod inner tube 2.1 is smaller than the outer diameter of the middle section, and the inner circles of the two ends of the composite material tie rod outer tube 2.2 are inverted cones; an annular positioning boss is provided on the end face of the shoulder bushing 3, and a straight-line positioning boss is provided in the axial direction of the shoulder bushing 3; four shoulder bushings 3 are respectively pre-buried in the ear holes of the double plug ears of the composite material joint 1; and two composite material joints 1 are respectively formed at the two ends of the composite material tie rod body 2.

[0006] Furthermore, the outer circle of the composite material joint 1 is an inverted cone with an angle of 175°.

[0007] The forming method of the integrated variable pitch tie rod comprises:

[0008] Step 1: using a composite material joint core mold, a composite material joint 1 is formed by a rotation method, wherein T700 is selected as the three-dimensional braided material, and when the composite material joint is preformed to a corresponding position, a boss bushing 3 is placed and the boss bushing 3 is positioned, and after forming, the composite material joint 1 is RTM-cured as a whole to finally form the composite material joint 1;

[0009] Step 2: Use the composite material tie rod body core mold to roll and form the composite material tie rod body inner tube 2.1. The material used for rolling and forming the inner tube is high temperature curing epoxy resin unidirectional carbon fiber prepreg CCM55J. After the composite material tie rod body tube 2.1 is rolled, it is sealed with a perforated isolation film, and the sealing bag is vacuumed. Then, the composite material tie rod body tube 2.1 is transferred to a curing furnace for hanging and curing;

[0010] Step 3: After the composite tie rod body inner tube 2.1 is cured at high temperature, the end surface is machined and the outer surface of the cylinder is polished until the coaxiality between the composite tie rod body inner tube 2.1 and the composite tie rod body core mold is ≤Φ0.1mm, and finally the composite tie rod body inner tube 2.1 is formed;

[0011] Step 4: Use a room temperature curing 230°C resistant structural adhesive to bond the composite joint 1 to the composite tie rod body inner tube 2.1, wrap them with adhesive-coated PTFE cloth after bonding, and then cure them at room temperature for 24 hours;

[0012] Step 5: Using the integrated composite material joint 1 and the composite material tie rod body tube 2.1 after curing in step 4 as the core mold, further winding to form the composite material tie rod body tube 2.2, the winding outer tube uses 2 bundles of CCM55J fibers, and the composite material tie rod body tube 2.2 is sealed with a perforated isolation film after winding, and transferred to a high-temperature curing furnace for curing;

[0013] Step 6: Machining the integrated variable pitch tie rod formed in step 5 until the final size requirement is reached.

[0014] Furthermore, in step 2, the laying method of the roll-formed inner tube is [45 / 05 / 902 / 05 / -45 / 05 / 90 / 05 / 45 / 05 / -45 / 05 / 90 / 05 / 45 / 05 / -45 / 05 / 902], and 12# BOPP tape is used for pre-compaction every 5 layers, and the pre-tightening material tension is ensured to be 3.5±0.2kg during the compaction process.

[0015] Further, in step 2, the sealed bag is vacuumed, specifically:

[0016] The vacuum degree shall not be less than 0.097MPa and the vacuum gauge reading shall not drop by more than 0.002Mpa within 5 minutes.

[0017] Furthermore, in step 5, during the winding process, the fiber tension of the two bundles of CCM55J fibers is not less than 15N.

[0018] Further, in step 5, the winding forming angle is;

[0019] [±104 / 90 / ±104 / 90 / ±104 / 90 / ±102 / 903].

[0020] Furthermore, the curing curve in step 2 is specifically:

[0021]

[0022] Furthermore, the curing curve in step 5 is specifically:

[0023]

[0024] Beneficial effects:

[0025] The rod body and rod joint of the integrated variable pitch rod are designed with full composite materials. Compared with the previous metal rods, the weight is significantly reduced, and the overall lightweight design requirements are met. At the same time, the integrated variable pitch rod has the advantages of high tensile and compressive modulus, strong environmental adaptability, high bending stiffness, and high joint strength, which fully meet the use requirements of helicopter variable pitch rods. In addition, the integrated design reduces the number of parts to be disassembled and installed, simplifies the work process, reduces product differences caused by human factors, and product consistency can be guaranteed. It avoids the bonding of composite materials and metal materials, reduces the use of shank spherical bearings, and greatly increases product reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of an integrated variable pitch tie rod;

[0027] Figure 2 This is a schematic diagram of the inner tube of the composite material pull rod of the present invention;

[0028] Figure 3 is a schematic diagram of a composite material joint of the present invention;

[0029] Figure 4 is a schematic diagram of a shoulder bushing of the present invention;

[0030] Figure 5 This is a diagram of the integrated variable pitch tie rod forming process.

[0031] Among them, there are two composite material joints 1, a composite material tie rod body 2, four shoulder bushings 3, a composite material tie rod inner tube 2.1 and a composite material tie rod outer tube 2.2. DETAILED DESCRIPTION

[0032] The integrated variable pitch tie rod body of the present invention is directly connected to the composite material double-plug ear joint during the processing process, avoiding the problem of unstable bonding performance between the metal joint and the composite material and low threaded connection strength between the shank spherical bearing and the metal joint. At the same time, the number of parts such as the connecting nut, the toothed washer, and the shank spherical bearing is reduced in the structural design, and the process of installing the toothed washer and the shank spherical bearing is omitted, effectively avoiding product defects caused by human factors.

[0033] like Figure 1-4 An integrated variable pitch tie rod comprises: a composite material joint 1, a composite material tie rod body 2, and a boss bushing 3. The composite material joint 1 is directly pre-embedded with a boss bushing 3 during processing using a three-dimensional weaving molding process.

[0034] The composite rod body 2 comprises an inner tube and an outer tube, wherein the outer diameter of the inner tube end portion is smaller than the outer diameter of the middle portion; high-strength carbon fiber material with a strength greater than 300 MPa in a 90° direction is wound around the outer sides of both ends of the outer tube.

[0035] The composite rod body 2 is formed by rolling and winding processes. After the inner tube is processed, the composite joint 1 is bonded, and then the inner tube of the composite rod body 2 and the composite joint 1 are wound together.

[0036] The integrated variable pitch tie rod of the present invention has the advantages of low weight, high strength, high modulus and high stability. The weight of the composite tie rod after forming is about 2kg, the equivalent modulus is about 200GP, the critical yield stress is about 12Kn, and all the performances are improved to varying degrees compared with the metal tie rod.

[0037] The composite material joint 1 and the composite material tie rod body 2 of the integrated composite material tie rod of the present invention are connected by composite materials and composite materials, and the connection strength and stability are better than the composite material-metal connection. In addition, the integrated composite material tie rod omits the connecting nut, toothed washer, and shank spherical bearing in the design, and the structure is greatly simplified.

[0038] The integrated composite tie rod composite joint 1 and composite tie rod body 2 of the present invention are hollow, and the core mold passes through the hollow area during the composite molding process. The metal core mold needs to be demolded after the composite material is molded, and the hollow design reserves a demolding space, and there is no need to use a degradable core mold. In addition, the existence of the core mold can provide a fixture space during the processing process, while ensuring the straightness during the processing process.

[0039] The end face of the integrated composite tie rod composite joint 1 of the present invention has an inverted cone of 175°, and after being wrapped around the outer tube of the composite tie rod body 2, the outer tube of the composite tie rod body 2 also has an inverted cone shape. When the composite tie rod is subjected to tension, the tension is decomposed at the composite joint 1 into tension along the composite tie rod body 2 and pressure perpendicular to the end face of the composite joint 1. Due to the presence of the inverted cone, the composite joint 1 and the composite tie rod body 2 are continuously pressed, which effectively prevents the composite joint 1 and the composite tie rod body 2 from debonding during the tension of the composite tie rod.

[0040] The integrated composite rod composite joint 1 of the present invention has an inward boss on its inner surface, and the boss is directly fixedly connected to the composite rod body 2. When the composite rod is subjected to pressure, the pressure on the composite joint 1 is directly transmitted to the composite rod body 2 by the outer surface of the composite joint 1 and the boss surface, and the composite rod body 2 is the main component subjected to pressure. The boss design of the composite joint 1 and the composite rod body 2 ensures that the composite rod meets the strength requirements during the compression process.

[0041] The integrated composite rod composite joint 1 of the present invention adopts a double-plug-in form, which reserves a core mold space and provides more choices for interface design. The structure connected to the composite joint 1 can adopt a single plug-in with a joint bearing, and the combination of the two provides three-directional rotational freedom; it can also adopt a double-plug-in form, and the combination of the two provides one-directional rotational freedom.

[0042] The integrated composite tie rod shoulder bushing 3 of the present invention has two positioning bosses, which limit the axial and circumferential movement of the shoulder bushing 3, effectively avoiding the problem of bushing slippage / slipping out. Since the composite joint 1 adopts a three-dimensional weaving process, the shoulder bushing 3 can be pre-embedded during the weaving process and integrally formed with the composite joint 1, avoiding the problem that the shoulder bushing 3 with bosses cannot be installed later.

[0043] The integrated composite tie rod forming process of the present invention includes a three-dimensional woven composite joint 1, a high temperature cured composite joint 1, a roll-formed composite tie rod body 2 inner tube, a high temperature cured composite tie rod body 2 inner tube, a machined composite tie rod body 2 inner tube, a bonded composite tie rod body 2 inner tube and a composite joint 1, a winding formed composite tie rod body 2 outer tube, and the composite tie rod is overall high temperature cured and overall machined.

[0044] like Figure 5 , the specific molding process and process are as follows:

[0045] Step 1: Process the core mold of the composite material joint 1 for three-dimensional braiding. Note that there is a 135° inverted cone from the core mold polished rod to the ear. Subsequently, the composite material joint 1 is formed by the rotation method, and T700 is selected as the three-dimensional braiding material. The boss bushing 3 is placed at the corresponding position of the preformed composite material joint 1 and accurately positioned by the mold. After forming, the composite material joint 1 is cured by RTM as a whole, and finally the composite material joint 1 is formed as shown in FIG. Figure 3 .

[0046] Step 2: Process the core mold of the composite tie rod body 2, which should have the characteristics of high rigidity and clampability. Then roll and form the composite tie rod body inner tube 2.1. The rolled inner tube material uses high temperature cured epoxy resin unidirectional carbon fiber prepreg (CCM55J), and the layering method is [45 / 05 / 902 / 05 / -45 / 05 / 90 / 05 / 45 / 05 / -45 / 05 / 90 / 05 / 45 / 05 / -45 / 05 / 902], and 12# BOPP tape is used for pre-compaction every 5 layers. During the compaction process, the pre-tightening material tension is guaranteed to be 3.5±0.2kg. After the composite tie rod body tube (2.1) is rolled, it is sealed with a perforated isolation film, and the sealing bag is evacuated (the vacuum degree is not less than 0.097MPa), and the vacuum gauge reading is guaranteed to drop by no more than 0.002Mpa within 5 minutes. Then the composite material tie rod body tube 2.1 is transferred into the curing furnace for hanging and curing. The curing curve is as follows:

[0047]

[0048] Step 3: After the composite material tie rod body tube 2.1 is cured at high temperature, the end face is machined and the outer surface of the cylindrical surface is polished. After the grinding machine processing, the coaxiality of the composite material tie rod body tube 2.1 and the core mold is ≤Φ0.1mm, and finally the composite material tie rod body tube 2.1 is formed. Figure 2 .

[0049] Step 4: Use a room temperature curing 230°C resistant structural adhesive to bond the composite joint 1 and the composite tie rod body inner tube 2.1, wrap it with adhesive-tipped PTFE cloth after bonding to prevent resin from flowing in during curing, and then cure it at room temperature for 24 hours.

[0050] Step 5: Using the integrated composite joint 1 and the composite tie rod body inner tube 2.1 in step 4 as the core mold, further winding is performed to form the composite tie rod body outer tube 2.2. The winding outer tube uses CCM55J fiber (2 bundles), the fiber tension is controlled to be no less than 15N, and the winding angle is [±104 / 90 / ±104 / 90 / ±104 / 90 / ±102 / 903]. After the composite tie rod body outer tube 2.2 is wound, it is sealed with a perforated isolation film and transferred to a high-temperature curing furnace for curing. The curing curve is as follows:

[0051]

[0052] Step 6: Machine the initially formed integrated variable pitch tie rod to achieve the final size requirements.

[0053] The key points of the present invention are:

[0054] The integrated composite material pull rod of the present invention has only one part after being formed, thereby eliminating the human uncertainty factor in the disassembly and assembly of the parts, omitting the threaded connection between the shank spherical bearing and the joint, and greatly improving the connection strength.

[0055] The integrated composite tie rod joint and the rod body material are both composite materials. Compared with metal joints, the bonding performance can be guaranteed.

[0056] The integrated composite tie rod and composite joint adopt a three-dimensional weaving process, the inner tube of the composite tie rod adopts a rolling forming process, and the outer tube of the composite tie rod after the bonding joint adopts a winding forming process. The process flow is clear and the reliability and credibility are high.

Claims

1. An integrated variable pitch pull rod, characterized in that: include: Two composite material joints (1), a composite material tie rod body (2), and four shoulder bushings (3), wherein: The composite material joint (1) is made of T700, is hollow in the axial direction, and comprises, from the inside to the outside, a large inner diameter section, a small inner diameter section and a double plug-in ear, wherein an inward boss is formed at the connection between the large inner diameter section and the small inner diameter end; the outer circle of the composite material joint (1) is an inverted cone; the composite material tie rod body (2) is made of CCM55J, and the composite material tie rod body (2) comprises a composite material tie rod inner tube (2.1) and a composite material tie rod outer tube (2.2), wherein the outer diameter of the end of the composite material tie rod inner tube (2.1) is smaller than the outer diameter of the middle section, and the inner circles of both ends of the composite material tie rod outer tube (2.2) are inverted cones; the end surface of the shoulder bushing (3) is provided with an annular positioning boss, and the axial direction of the shoulder bushing (3) is provided with a straight-line positioning boss; four shoulder bushings (3) are respectively pre-buried in the ear holes of the double plug-in ears of the composite material joint (1); and two composite material joints (1) are respectively formed at the two ends of the composite material tie rod body (2).

2. The integrated variable pitch pull rod according to claim 1, characterized in that: The outer circle of the composite material joint (1) is an inverted cone with an angle of 175 degrees.

3. The forming method of the integrated variable pitch tie rod is characterized in that: include: Step 1: using a composite material joint core mold, a composite material joint (1) is formed by a rotation method, wherein the three-dimensional braided material is T700, and when the composite material joint is preformed to a corresponding position, a boss bushing (3) is placed and the boss bushing (3) is positioned, and after forming, the composite material joint (1) is RTM-cured as a whole, and finally the composite material joint (1) is formed; Step 2: using a composite material tie rod body core mold to roll and form a composite material tie rod body inner tube (2.1), the material used for rolling and forming the inner tube is high temperature curing epoxy resin unidirectional carbon fiber prepreg CCM55J, after the composite material tie rod body tube (2.1) is rolled and sealed with a perforated isolation film, the sealing bag is evacuated, and then the composite material tie rod body tube (2.1) is transferred to a curing furnace for hanging and curing; Step 3: After the composite tie rod body inner tube (2.1) is cured at high temperature, the end surface is machined and the outer surface of the cylindrical surface is polished until the coaxiality between the composite tie rod body inner tube (2.1) and the composite tie rod body core mold is ≤Φ0.1mm, and finally the composite tie rod body inner tube (2.1) is formed; Step 4: Use a room temperature curing 230°C resistant structural adhesive to bond the composite material joint (1) to the composite material tie rod body inner tube (2.1), and then wrap it with adhesive-coated polytetrafluoroethylene cloth after bonding, and then cure it at room temperature for 24 hours; Step 5: Using the integrated composite material joint (1) and the composite material tie rod body inner tube (2.1) after curing in step 4 as a core mold, further winding to form a composite material tie rod body outer tube (2.2), wherein the winding outer tube uses 2 bundles of CCM55J fibers, and after winding, the composite material tie rod body outer tube (2.2) is sealed with a perforated isolation film and transferred to a high-temperature curing furnace for curing; Step 6: Machining the integrated variable pitch tie rod formed in step 5 until the final size requirement is reached.

4. The method according to claim 3, characterized in that: In step 2, the laying method of the inner tube formed by rolling is: [45 / 05 / 902 / 05 / -45 / 05 / 90 / 05 / 45 / 05 / -45 / 05 / 90 / 05 / 45 / 05 / -45 / 05 / 902], and use 12# BOPP belt for pre-compaction every 5 layers, and ensure the pre-tightening material tension is 3.5±0.2kg during the compaction process.

5. The method according to claim 3, characterized in that: In step 2, the sealed bag is evacuated, specifically: The vacuum degree shall not be less than 0.097MPa and the vacuum gauge reading shall not drop by more than 0.002Mpa within 5 minutes.

6. The method according to claim 3, characterized in that In step 5, during the winding process, the fiber tension of the two bundles of CCM55J fibers is not less than 15N.

7. The method according to claim 3, characterized in that In step 5, the winding forming angle is [±104 / 90 / ±104 / 90 / ±104 / 90 / ±102 / 903].

8. The method according to claim 3, characterized in that The curing curve in step 2 is as follows:

9. The method according to claim 3, characterized in that: The curing curve in step 5 is as follows:

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