A detachable mandrel for filament winding an engine casing and a method of designing the same

Abstract

The application discloses a detachable core mould of a fiber-wound engine shell and a design method thereof. The core mould comprises a core shaft extending in an axial direction, a split metal framework sleeved outside the core shaft, a bushing matched with an inner wall of the metal framework, a key block embedded between the core shaft and the metal framework, a framework pressing nut and front and rear head fixing mechanisms located at two ends of the core shaft. The outer surface of a cylinder segment part of the metal framework is matched with an inner profile of a heat insulation layer. The core mould can be taken out after the shell is formed, and has the characteristics of reliable positioning, good rigidity and reusability.

Description

Technical Field

[0001] This invention relates to the field of composite material engine housing molding tooling technology, specifically to a detachable mandrel for fiber-wound engine housing and its design method. Background Technology

[0002] Fiber-wound engine casings typically include a front end cap, a rear end cap, a cylindrical insulation layer, and an external fiber composite load-bearing layer. During the molding process, a mandrel is required to support and position the inner surface of the insulation layer and the front and rear end caps, and to withstand fiber winding tension, curing temperature changes, and handling and clamping loads.

[0003] In existing small or medium-sized fiber-wound engine housings, sand core molds, plaster core molds, soluble core molds, or disposable combined core molds are commonly used as internal supports. While these core molds are easy to remove after the housing has cured, they typically suffer from low reusability, long manufacturing cycles, limited rigidity during the molding process, and significant dimensional instability of the internal surface due to process variations. For engine housings with small openings in the front and rear end caps and large cylinder diameters, using a single metal core mold directly makes it difficult to remove the core mold from the cured housing cavity; while using only segmented metal core molds can easily lead to problems such as unreliable segment positioning, circumferential movement during the winding process, interference during disassembly after curing, and insufficient precision in repeated assembly.

[0004] Therefore, it is necessary to provide a fiber-wound engine housing core mold that takes into account the rigidity of the metal core mold, the ability to disassemble the segments, the reliability of the end cap positioning, and the reusability, and to establish a corresponding design verification method. Summary of the Invention

[0005] The purpose of this application is to overcome the above-mentioned technical deficiencies and propose a detachable mandrel for fiber-wound engine housing and its design method, thereby solving the technical problems of long manufacturing cycle, low reusability, inconvenient demolding, and insufficient structural rigidity of existing small fiber-wound engine housing mandrels.

[0006] To achieve the above-mentioned technical objectives, this application adopts the following technical solution: In a first aspect, this application provides a detachable mandrel for a fiber-wound engine housing, comprising: A mandrel, which extends along its axial direction; A metal skeleton is fitted on the outside of the mandrel and has a cylindrical section. The outer surface of the cylindrical section is a continuous support surface that is adapted to the inner surface of the insulation layer. The metal skeleton is a detachable segmented structure and includes multiple segmented parts that are distributed circumferentially and enclose the cylindrical section. A bushing is fitted onto the mandrel, and the outer peripheral positioning surface of the bushing mates with the inner wall positioning surface of the metal frame. Key blocks, which are embedded in the corresponding keyways of the mandrel and the metal skeleton; A skeleton clamping nut, which is threaded to the mandrel and clamps the metal skeleton axially directly or via the bushing; A front end cap fixing mechanism is provided at the front end of the mandrel. The front end cap fixing mechanism has a front positioning kit that mates with the inner hole of the front end cap of the engine housing and a front axial locking member that is connected to the mandrel. A rear end cap fixing mechanism is provided at the rear end of the mandrel. The rear end cap fixing mechanism has a rear positioning kit that mates with the inner hole of the rear end cap of the engine housing and a rear axial locking member connected to the mandrel.

[0007] In some embodiments of this application, the front end cap includes a front connector, the front positioning kit includes a front connector positioning sleeve, and the front axial locking member includes a front connector connecting screw, a thrust ball bearing, and a front connector locking nut; the front connector positioning sleeve has an outer positioning surface that mates with the inner hole of the front end cap, the front connector connecting screw passes through the front connector positioning sleeve and is connected to the front connector of the front end cap; the thrust ball bearing is sandwiched between the front connector locking nut and the front connector positioning sleeve; the front connector locking nut is threadedly connected to the mandrel; The rear end cap includes a rear connector, the rear positioning kit includes a rear connector positioning sleeve, and the rear axial locking component includes a rear connector connecting screw, a thrust ball bearing, and a rear connector locking nut. The rear connector positioning sleeve has an outer positioning surface that mates with the inner hole of the rear end cap. The rear connector connecting screw passes through the rear connector positioning sleeve and is connected to the rear connector of the rear end cap. The thrust ball bearing is sandwiched between the rear connector locking nut and the rear connector positioning sleeve. The rear connector locking nut is threadedly connected to the mandrel.

[0008] In some embodiments of this application, the mandrel includes a mandrel body and a connecting disc. The connecting disc is disposed on one axial side of the mandrel body and has an axial positioning end face facing the metal frame. The axial positioning end face of the connecting disc abuts against one end of the metal frame.

[0009] In some embodiments of this application, at least one of the segmented members is an inward-pointing V-shaped segment, and the radially outer sides of each segmented member together form the continuous support surface.

[0010] In some embodiments of this application, the metal frame includes an inward-pointing V-shaped segment and an outward-pointing V-shaped segment. The two lateral parting surfaces of the inward-pointing V-shaped segment are inclined relative to the radial reference surface passing through the circumferential center of the inward-pointing V-shaped segment, such that the inward-pointing V-shaped segment has a wedge-shaped radial cross-section, and its circumferential width decreases from the outer surface of the cylindrical section towards the mandrel. The outward-pointing V-shaped segment is arranged adjacent to the inward-pointing V-shaped segment, and the circumferential width of the outward-pointing V-shaped segment increases from the outer surface of the cylindrical section towards the mandrel. The lateral parting surfaces of adjacent outward-pointing V-shaped segments cooperate with the lateral parting surfaces of inward-pointing V-shaped segments to form an inclined parting interface.

[0011] In some embodiments of this application, the lateral parting surface of the inward-pointing V-shaped structure is tilted at an angle of 10° to 20° relative to the corresponding radial reference surface.

[0012] In some embodiments of this application, the metal skeleton is an eight-lobed structure, wherein four lobes are inward-facing and the other four lobes are outward-facing; each lobe is provided with ribs extending axially on its inner side, and the metal skeleton is made of low-alloy structural steel, wherein the total content of alloying elements in the low-alloy structural steel is not greater than 5%.

[0013] In some embodiments of this application, the key block includes a first key block and a second key block. The first key block is embedded between the mandrel and the metal frame, and the second key block is embedded between the mandrel and the rear connector positioning sleeve. The two sets of side surfaces of the first key block abut against the keyway wall of the mandrel and the keyway wall of the metal frame, respectively. The two sets of side surfaces of the second key block abut against the keyway wall of the mandrel and the keyway wall of the rear connector positioning sleeve, respectively.

[0014] In some embodiments of this application, the bushing includes an inner hole that mates with the outer periphery of the mandrel, an outer peripheral positioning surface that mates with the inner wall of the metal frame, and an axial end face for the frame clamping nut to press against; the frame clamping nut is threadedly connected to the mandrel, and the frame clamping nut presses against the bushing or the metal frame axially, so that the metal frame, the bushing, the key block, and the mandrel form an axially clamping and circumferentially limiting assembly.

[0015] Secondly, this application also provides a design method for a detachable mandrel of a fiber-wound engine housing, used to design a detachable mandrel of a fiber-wound engine housing as described in any embodiment of the first aspect, comprising the following steps: The initial structural scheme of the mandrel and metal frame is determined based on the engine housing parameters. The metal frame includes multiple circumferentially distributed and enclosed segments to form a cylindrical section, and includes at least an inward-pointing segment. The metal frame was disassembled and simulated for verification, confirming that there was no interference in the disassembly path; The stress and strain of the segmented metal skeleton under fiber tension and curing thermal stress were calculated and analyzed using finite element software. The strength and stiffness of the metal skeleton are optimized iteratively using preset stress and strain thresholds; The core mold was fabricated according to the optimized scheme, and the fiber-wound shell was fabricated and tested for bursting.

[0016] Compared with the prior art, the beneficial technical effects of the technical solution provided in this application include: The detachable metal mandrel of this application uses a mandrel as the central assembly reference and a segmented metal skeleton to form the supporting foundation for the inner surface of the insulation layer. Bushings, key blocks, and skeleton clamping nuts respectively form radial positioning, circumferential limiting, and axial clamping structures. The front and rear end cap fixing mechanisms respectively mate with the inner holes of the front and rear end caps and lock with the mandrel, making the end caps, metal skeleton, and mandrel form a relatively stable molding tooling assembly. The mandrel has good supporting rigidity and positioning reliability during fiber winding and curing, and can be disassembled and reused after molding due to the segmented structure. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this application, the accompanying drawings used in the embodiments will be briefly described below: Figure 1 This is a schematic diagram of the structure of a fiber-wound engine casing.

[0018] Figure 2 This is a schematic diagram of the overall structure of the detachable core mold.

[0019] Figure 3 This is a schematic diagram of the mandrel structure.

[0020] Figure 4 This is a schematic diagram of the segmented structure of the metal skeleton.

[0021] Figure label: 1-Mandrel; 11-Mandrel body; 12-Connecting disc; 2-Metal frame; 21-Inward-facing lobed structure; 22-Outward-facing lobed structure; 3-Bushing; 41 - First key block; 42 - Second key block; 5-Frame clamping nut; 61-Front connector positioning sleeve; 62-Front connector connecting screw; 63-Front connector lock nut; 71-Rear connector positioning sleeve; 72-Rear connector connecting screw; 73-Rear connector lock nut; 8-Front connector; 9-Rear connector; 10 - Insulation layer; 20 - Engine housing; 30 - Thrust ball bearing. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] Those skilled in the art will understand that, in this specification, the term "comprising" is an open-ended expression, meaning that the stated feature is present but other features are excluded. Directional terms such as "upper," "lower," "left," and "right" refer to exemplary directions based on the accompanying drawings. Features specified as "first" or "second" implicitly include one or more of that feature. Singular expressions can also be used in plural forms. "Multiple" means two or more. The terms "installed," "connected," and "linked" can refer to a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection via an intermediate medium, and it can be a connection within two components. Furthermore, "linked" can include wireless connections.

[0024] See Figures 1 to 4 A detachable metal mandrel for a fiber-wound engine housing includes a mandrel 1, a metal frame 2, a bushing 3, a key block, a frame clamping nut 5, a front end fixing mechanism, and a rear end fixing mechanism.

[0025] The mandrel 1 extends along its axial direction, serving as the central support and assembly reference component for the entire mandrel mold. The mandrel 1 can be a solid shaft or, depending on weight, rigidity, and machine tool clamping requirements, can be configured as a partially hollow shaft. Both ends of the mandrel 1 can be provided with shaft sections and threaded sections that mate with winding equipment, support seats, or lock nuts.

[0026] The metal frame 2 is fitted onto the outside of the mandrel 1. The metal frame 2 has a cylindrical section, the outer surface of which is a continuous support surface that matches the inner surface of the insulation layer 10. The continuous support surface can be a cylindrical surface, a cylindrical surface with a transition arc, or a combined curved surface that connects with the transition area of ​​the front and rear end caps. The metal frame 2 adopts a detachable segmented structure, with each segment forming the cylindrical section in the assembled state, and can be removed from the inner cavity of the engine housing 20 after it is formed.

[0027] Bushing 3 is fitted onto mandrel 1. The inner hole of bushing 3 mates with the outer circumference of mandrel 1, and the outer circumferential positioning surface of bushing 3 mates with the inner wall positioning surface of metal skeleton 2. Bushing 3 can be configured as a cylindrical positioning sleeve, or a stepped positioning surface can be provided according to the shape of the inner cavity of metal skeleton 2. Key blocks are embedded in the corresponding keyways of mandrel 1 and metal skeleton 2, thereby restricting metal skeleton 2 in the circumferential direction relative to mandrel 1. Skeleton clamping nut 5 is threaded to mandrel 1 and directly presses against metal skeleton 2, or presses against metal skeleton 2 through bushing 3, thereby clamping metal skeleton 2 axially.

[0028] The front end cap fixing mechanism is located at the front end of the mandrel 1. The front end cap fixing mechanism has a front positioning kit that mates with the inner hole of the front end cap and a front axial locking member connected to the mandrel 1. The rear end cap fixing mechanism is located at the rear end of the mandrel 1. The rear end cap fixing mechanism has a rear positioning kit that mates with the inner hole of the rear end cap and a rear axial locking member connected to the mandrel 1. The front and rear end caps are kept coaxial with the mandrel 1 by corresponding positioning kits, and form an integral assembly with the metal frame 2 and the mandrel 1 by corresponding axial locking members.

[0029] Working principle: Mandrel 1 provides a central reference, metal frame 2 provides rigid support consistent with the inner surface of insulation layer 10, bushing 3 reduces assembly eccentricity of metal frame 2, key block restricts the rotation of metal frame 2 relative to mandrel 1 during winding, and frame clamping nut 5 forms axial clamping. The front end fixing mechanism and rear end fixing mechanism control the positions of the front and rear end caps respectively. This structure ensures a relatively stable assembly relationship of the mandrel during fiber winding and curing, and allows for disassembly in segments after molding, thereby improving the reusability of the mandrel.

[0030] The rubber at the front connector is molded with the front connector to form a front end cap. The front end cap fixing mechanism includes a front connector positioning sleeve 61, a front connector connecting screw 62, a thrust ball bearing 30, and a front connector locking nut 63. The front connector positioning sleeve 61 has an outer positioning surface that mates with the inner hole of the front end cap. When the front end cap is formed by molding the front connector 8 and the rubber at the front connector, the front connector positioning sleeve 61 can extend into the inner hole of the front end cap and form a coaxial positioning with the front connector 8. This inner hole is the inner hole of the front connector 8. The front connector connecting screw 62 passes through the front connector positioning sleeve 61 and mates with the threaded hole or connecting hole on the front connector 8. The thrust ball bearing 30 is sandwiched between the front connector locking nut 63 and the front connector positioning sleeve 61. The front connector locking nut 63 is threadedly connected to the front threaded section of the mandrel 1.

[0031] The rubber at the rear connector is molded with the rear connector to form a rear end cap. The rear end cap fixing mechanism includes a rear connector positioning sleeve 71, a rear connector connecting screw 72, a thrust ball bearing 30, and a rear connector locking nut 73. The rear connector positioning sleeve 71 has an outer positioning surface that mates with the inner hole of the rear end cap. When the rear end cap is formed by molding the rear connector 9 and the rubber at the rear connector, the rear connector positioning sleeve 71 can extend into the inner hole of the rear end cap and form a coaxial positioning with the rear connector 9. This inner hole is the inner hole of the rear connector 9. The rear connector connecting screw 72 passes through the rear connector positioning sleeve 71 and mates with the connecting hole on the rear connector 9. The thrust ball bearing 30 is sandwiched between the rear connector locking nut 73 and the rear connector positioning sleeve 71. The rear connector locking nut 73 is threadedly connected to the rear threaded section of the mandrel 1.

[0032] When the front connector locking nut 63 and the rear connector locking nut 73 are tightened, the axial locking force is transmitted to the positioning sleeve via the corresponding thrust ball bearings. The thrust ball bearings convert the end-face sliding friction during nut rotation into rolling friction, reducing the tendency of the positioning sleeve to twist with the nut, thus making the axial clamping process of the front and rear end caps smoother. The front connector connecting screw 62 and the rear connector connecting screw 72 respectively form a detachable connection between the positioning sleeve and the corresponding connector, which is beneficial for end cap positioning and subsequent disassembly.

[0033] The mandrel 1 includes a mandrel body 11 and a connecting disc 12. The mandrel body 11 is a main component extending axially, and the connecting disc 12 is disposed on one axial side of the mandrel body 11. The connecting disc 12 can be integrally machined with the mandrel body 11, or it can be fixed to the mandrel body 11 by welding, threading, interference fit, or fasteners. The connecting disc 12 has an axial positioning end face facing the metal frame 2, which abuts against one end of the metal frame 2. The connecting disc 12 may also be provided with a stop, positioning step, or partial mating surface to improve the consistency of the assembly position of the end of the metal frame 2.

[0034] When the metal frame 2 is installed on the mandrel 1, one end is axially positioned by the connecting plate 12, and the other end is clamped by the bushing 3 and the frame clamping nut 5. The connecting plate 12 provides a fixed end reference, which can reduce the axial misalignment of the segmented parts and make it easier to maintain a consistent continuous support profile in the cylinder section.

[0035] The metal frame 2 includes multiple segmented members distributed circumferentially and enclosing to form a cylindrical section. The radially outer sides of each segmented member together form a continuous support profile. At least one segmented member is an inward-pointing segmented member 21. The inward-pointing segmented member 21 can be located at one or more circumferential positions of the metal frame 2, and its lateral parting surface is inclined relative to the radial reference plane, so that it can first generate a tendency to separate from adjacent segmented members when moving radially.

[0036] The segmented components jointly bear the internal support load during the insulation layer 10 and fiber winding process. After curing, each segmented component can be removed from the inner cavity of the engine housing 20 in a predetermined order. The inward V-shaped structure of the segmented components 21 allows some segments to preferentially retract into the space where the mandrel 1 was originally located, freeing up disassembly space for other segments.

[0037] The metal frame 2 includes an inward-facing V-shaped segment 21 and an outward-facing V-shaped segment 22. The two lateral parting surfaces of the inward-facing V-shaped segment 21 are inclined relative to the radial reference plane passing through the circumferential center of the segment, making the inward-facing V-shaped segment 21 wedge-shaped in radial cross-section, with its circumferential width decreasing from the outer surface of the cylindrical section towards the mandrel 1. The outward-facing V-shaped segment 22 is adjacent to the inward-facing V-shaped segment 21, and its circumferential width in radial cross-section increases from the outer surface of the cylindrical section towards the mandrel 1. The lateral parting surfaces of adjacent outward-facing V-shaped segments 22 and inward-facing V-shaped segments 21 cooperate to form an inclined parting interface. In the assembled state, adjacent lateral parting surfaces can either fit together or retain a small clearance to meet processing, thermal expansion, and disassembly requirements.

[0038] After the mandrel 1 is removed, the inward-pointing V-shaped segment 21 can move back to the original space of the mandrel 1 and detach from the adjacent outward-pointing V-shaped segment 22. After the inward-pointing V-shaped segment 21 is removed, the adjacent outward-pointing V-shaped segment 22 gains circumferential loosening and attitude adjustment space. This inclined parting interface combines the support requirements of the metal frame 2 with the disassembly requirements of the small opening of the shell, reducing the possibility of interference when the segment is removed from the inner cavity.

[0039] The inclination angle of the lateral parting surface of the inward V-shaped structure segment 21 relative to the corresponding radial reference surface can be between 10° and 20°. This inclination angle is determined based on the inner diameter of the front end cap, the inner diameter of the rear end cap, and the outer diameter of the metal skeleton 2. When the inner diameter of the front end cap is smaller and the inner diameter of the rear end cap is larger, the inner diameter of the rear end cap can be prioritized as the main extraction channel, and the inclination angle can be determined in conjunction with the maximum external dimensions of the inward V-shaped structure segment 21. When the inner diameters of the front and rear end caps are similar, the inclination angle can be determined by comprehensively considering the extraction space at both ends, the strength of the segment, and the feasibility of machining.

[0040] If the tilt angle is too small, there will be insufficient space for the inward-pointing V-shaped structure's 21 segments to retreat; if the tilt angle is too large, the edge thickness and contact area of ​​the segments may be affected. Controlling the tilt angle between 10° and 20° achieves a suitable balance between disassembly space, support area, and segment strength.

[0041] In one specific structure, the metal skeleton 2 has an eight-petal structure, with four petals being inward-facing V-shaped segments 21 and the remaining four petals being outward-facing V-shaped segments 22. The inward-facing and outward-facing V-shaped segments 21 and 22 can be arranged alternately circumferentially, or locally adjusted according to the orientation of the openings in the front and rear end caps and the removal path. Each segment has axially extending stiffening plates on its inner side. These stiffening plates can be flat ribs, T-shaped ribs, or reinforcing ribs with weight-reducing holes, and their height and thickness are determined based on the outer diameter of the metal skeleton 2, the winding tension, and the curing conditions. The metal skeleton 2 can be made of Q345 low-alloy structural steel.

[0042] The eight-lobed structure allows for control of the circumferential width of individual lobes, facilitating adjustment and removal within small-opening shells; axial stiffeners enhance the bending and torsional resistance of the lobes under winding tension and curing heat load; Q345 low-alloy structural steel possesses good strength, machinability, and weldability, making it suitable for manufacturing reusable metal frames.

[0043] The key block includes a first key block 41 and a second key block 42. The first key block 41 is embedded between the mandrel 1 and the metal frame 2. The mandrel 1 has an axial keyway that mates with the first key block 41, and the metal frame 2 or its end connecting portion has a corresponding keyway. The two sets of side surfaces of the first key block 41 abut against the keyway wall of the mandrel 1 and the keyway wall of the metal frame 2, respectively. The second key block 42 is embedded between the mandrel 1 and the rear connector positioning sleeve 71. The two sets of side surfaces of the second key block 42 abut against the keyway wall of the mandrel 1 and the keyway wall of the rear connector positioning sleeve 71, respectively.

[0044] The first key block 41 bears the circumferential torque between the metal skeleton 2 and the mandrel 1, reducing the rotation of the metal skeleton 2 relative to the mandrel 1 during fiber winding. The second key block 42 keeps the rear connector positioning sleeve 71 circumferentially positioned relative to the mandrel 1, reducing angular displacement of the rear end cap during assembly and winding. The key block structure cooperates with the axial clamping structure of the nut, enabling the mandrel to transmit torque while maintaining its removability.

[0045] The bushing 3 includes an inner hole that mates with the outer circumference of the mandrel 1, an outer circumferential positioning surface that mates with the inner wall of the metal frame 2, and an axial end face for the frame clamping nut 5 to press against. The inner hole of the bushing 3 can be fitted onto the mandrel 1 with a clearance fit or a transition fit, i.e., a smaller clearance fit, so as to maintain good coaxial positioning while ensuring convenient assembly. The mating part between the outer circumferential positioning surface of the bushing 3 and the inner wall of the metal frame 2 can form a cylindrical surface or other rotational surface fit structure suitable for positioning. When the frame clamping nut 5 is tightened, its axial thrust acts on the axial end face of the bushing 3, and the bushing 3 then transmits this axial force to the metal frame 2, so that the metal frame 2, bushing 3, key block and mandrel 1 form an axial clamping and circumferential limiting assembly.

[0046] Bushing 3 combines radial positioning with axial force transmission, ensuring the relative positional relationship between the metal frame 2 and the mandrel 1, while also allowing the axial load of the clamping nut to be stably applied to the frame assembly. Structurally, bushing 3 serves a dual function of positioning and load transmission, which helps improve assembly stability.

[0047] This application also provides a design method for a detachable mandrel, used to design the aforementioned detachable mandrel for a fiber-wound engine housing.

[0048] During the design process, the initial structural scheme of the mandrel and metal frame is first determined based on the engine housing parameters. These parameters include the housing length, the inner diameter of the front end cap, the inner diameter of the rear end cap, the inner diameter of the insulation layer, and the inner surface profile of the insulation layer. The metal frame adopts a segmented structure, comprising multiple circumferentially distributed segments that enclose and form the cylindrical section, and includes at least an inward-pointing V-shaped segment.

[0049] Subsequently, a disassembly simulation was conducted on the metal frame to confirm that the movement paths of each segmented component did not interfere with the predetermined disassembly sequence. The disassembly simulation can be carried out based on a 3D model, focusing on verifying the feasibility of prioritizing the disassembly of the inward-pointing segmented structure and the subsequent disassembly paths of the remaining segments.

[0050] After ensuring the structural descratization requirements are met, finite element analysis software is used to calculate and analyze the stress and strain of the segmented metal skeleton under fiber tension and curing thermal stress. The fiber tension and curing temperature conditions can be input based on the winding process parameters to be used.

[0051] The strength and stiffness of the metal skeleton are then optimized iteratively using preset stress and strain thresholds. Optimization variables may include the number of segments, stiffener dimensions, parting line angle, skeleton wall thickness, and local reinforcement methods. Finally, a core mold is fabricated according to the optimized scheme, and a fiber-wound shell is manufactured and subjected to burst testing.

[0052] By combining disassembly verification with load-bearing capacity analysis, the design scheme is gradually converged through structural design, simulation verification, and physical verification. Adopting this design method improves the relevance and feasibility of the core mold design.

[0053] Specifically, S1, determine the spindle diameter and length based on structural parameters such as the length of the engine housing, the inner hole of the front end cap, and the inner hole of the rear end cap; S2. Determine the metal frame structure scheme and material selection based on the inner diameter of the engine casing insulation and the inner surface of the insulation layer. S3. Determine the metal frame connection and fixing method and the number of segments based on parameters such as the mandrel structure, the inner hole of the front end cap, and the inner hole of the rear end cap. S4. Determine the structure of the bushing and the metal skeleton locking nut based on the front end cap structure; S5. Based on the front connector structure, determine the front connector positioning sleeve, the thrust ball bearing that is connected and fixed to the spindle, and the front connector locking nut structure. S6. Based on the structure of the rear connector, determine the structure of the rear connector positioning sleeve, the thrust ball bearing that is connected and fixed to the spindle, and the rear connector locking nut. S7. Conduct detailed structural design based on the determined plan, and verify the metal frame demolding using CAD design software. S8. The stress and strain of the metal skeleton after segmentation under fiber tension and thermal stress during curing were calculated and analyzed using finite element software. S9. Optimize and iterate the strength and stiffness of the metal skeleton based on the CAE finite element analysis results.

[0054] S10. Based on the optimized design scheme, produce the core mold physical object; S11. Use the manufactured mandrel to fabricate a fiber-wound engine housing, verifying the manufacturing process, demolding process, mold strength and rigidity, and reassembly performance. S12. Conduct a burst test on the fabricated wound engine casing.

[0055] In one specific application, the rubber at the front joint is molded with the front joint to form a front end cap, and the rubber at the rear joint is molded with the rear joint to form a rear end cap. After the front and rear end caps are formed, they are respectively connected and fixed to the mandrel 1 and the metal frame 2 using the front joint positioning sleeve 61, the front joint connecting screw 62, the thrust ball bearing 30, the front joint locking nut 63, the rear joint positioning sleeve 71, the rear joint connecting screw 72, the second key block 42, the thrust ball bearing 30, and the rear joint locking nut 73.

[0056] First, the end cap and corresponding connector are integrated. Then, a coaxial and axial clamping relationship is established with the mandrel assembly using a positioning sleeve, so as to form a complete and stable tooling state before winding. This helps to make the front and rear forming parts of the shell more coordinated with the mandrel assembly structure.

[0057] After the housing has completed fiber winding and curing, the following demolding process can be adopted: First, disassemble the locking components at the front and rear ends of the mandrel 1, including disassembling the front connector locking nut 63, thrust ball bearing 30, front connector positioning sleeve 61, rear connector positioning sleeve 71, and rear connector locking nut 73, etc., then disassemble the frame clamping nut 5 and bushing 3 to fix the engine housing, and pull the mandrel 1 out from the inner hole of the rear connector. After the mandrel 1 is pulled out, disassemble the segmented assembly of the metal frame 2, prioritizing the disassembly of the inward V-shaped structure segment 21, and then loosening the remaining outward V-shaped structure segments 22 in sequence before removing them from the inner cavity of the engine housing.

[0058] By first releasing the locking relationship at the end of the mandrel and pulling it out, the central support constraint is eliminated. Then, the circumferential interlocking relationship is released by prioritizing the disassembly of the inward-facing segmented structure. Finally, the remaining segmented parts are gradually removed. This improves the feasibility of demolding operations and reduces interference during disassembly.

[0059] In a specific design example, the length of a fiber-wound engine casing is 542mm, the casing diameter is φ400mm, and the design burst pressure is not less than 20.3MPa. The main structure includes a front joint, a rear joint, an insulation layer, and a fiber-wound layer.

[0060] Based on the shell length of 542mm, the inner diameter of the front end cap of φ120mm, and the inner diameter of the rear end cap of φ180mm, the mandrel diameter is determined to be φ85mm and the length to be 1350mm. Based on the insulation inner diameter of φ385mm and the inner surface of the insulation layer, the metal skeleton adopts an eight-lobed structure, with four lobes using an inward V-shape for demolding from inside the product. Axial stiffeners are provided on each lobe to improve the rigidity, strength, and torsional resistance of the lobe structure. Q345 low-alloy structural steel is selected as the material. Based on the mandrel length and the inner diameter of the front and rear end caps, the metal skeleton adopts a connection scheme where the rear end is assembled with the mandrel, the front end is positioned by bushing 3 and the first key block 41, and tightened by the skeleton clamping nut 5. Furthermore, based on the front and rear joint structures, the detailed structures of the front joint positioning sleeve 61, the rear joint positioning sleeve 71, and the corresponding thrust ball bearings and locking nuts are determined.

[0061] The assembly relationships of the mandrel, segmented frame, and end fixing mechanism are deduced based on the shell's dimensional parameters, while also considering load-bearing capacity under the premise of meeting demolding space requirements. Custom structural designs can be carried out for specific shell dimensions.

[0062] In the above design example, CAE finite element software was used to analyze the segmented metal skeleton. Under conditions of approximately 50N single-strand fiber tension, approximately 1.2MPa equivalent stress, and a curing temperature of 150℃, the stress and strain of the eight-segment metal skeleton were calculated and analyzed. Based on process requirements, the stress value of the metal skeleton was controlled within 50MPa, and the strain within 0.3mm. The strength and stiffness of the metal skeleton were then optimized iteratively.

[0063] By inputting typical winding tension and curing heat load, the mechanical response of the segmented structure in a real-world manufacturing environment is predicted, thereby guiding the optimization of the segment wall thickness, stiffener dimensions, and parting interface parameters. This helps improve the reliability of the structural design before fabrication.

[0064] The optimized mandrel was used to fabricate a fiber-wound engine casing, verifying the manufacturing process, demolding process, mold strength and rigidity, and reassembly performance. An explosion test was conducted on the completed wound engine casing, achieving a burst value of 24.3 MPa. Compared to the highest burst value of 22.2 MPa for a similar wound engine casing fabricated using a sand mandrel, this verifies the feasibility of the detachable metal mandrel solution.

[0065] A metal skeleton with higher stiffness and a more stable supporting surface is beneficial for tension control and molding consistency during the winding process, thereby contributing to the load-bearing capacity of the shell. The core mold structure of this application has good application value in actual manufacturing.

[0066] This application comprises a detachable mandrel assembly consisting of a mandrel, a segmented metal skeleton, bushings, key blocks, a skeleton clamping nut, and a front and rear end fixing mechanism. During assembly, the metal skeleton surrounds the mandrel, using bushings to establish radial positioning, key blocks to prevent circumferential rotation, and the skeleton clamping nut and connecting disc to form axial clamping. The front and rear end caps are connected to the mandrel assembly via positioning sleeves, connecting screws, thrust ball bearings, and locking nuts. After winding and curing, the end locking structure is first released and the mandrel is pulled out. Then, the inward-facing segmented structure is removed first, followed by the removal of the remaining segmented components, thus achieving demolding of the shell cavity.

[0067] Based on the above structure and method, this application can provide a reusable metal support profile in the molding of small fiber-wound engine housings. It has good strength, rigidity and turnover capacity, which is beneficial to the stable control of tension during the fiber winding process, the maintenance of the molding quality of the insulation layer and the winding layer, and the disassembly and demolding after curing. It is suitable for small engine housings with high production cycle requirements.

[0068] Those skilled in the art will understand that the steps, measures, and schemes in the various operations, methods, processes, and procedures discussed in this application can be alternated, modified, rearranged, decomposed, combined, or deleted.

[0069] The specific embodiments described above do not constitute a limitation on the scope of protection of this application. Any other corresponding changes and modifications made based on the technical concept of this application should be included within the scope of protection of the claims of this application.

Claims

1. A detachable mandrel for a fiber-wound engine housing, characterized in that, include: mandrel; A metal skeleton is fitted onto the outside of the mandrel and has a cylindrical section. The outer surface of the cylindrical section is a continuous support profile. The metal skeleton includes a plurality of circumferentially distributed and enclosing segments that form the cylindrical section. A bushing is fitted onto the mandrel, and the outer peripheral positioning surface of the bushing mates with the inner wall positioning surface of the metal frame. Key blocks are embedded in the corresponding keyways of the mandrel and the metal skeleton; A skeleton clamping nut is connected to the mandrel and directly or via the bushing clamps the metal skeleton axially. A front end cap fixing mechanism is provided at the front end of the spindle. The front end cap fixing mechanism has a front positioning kit that mates with the inner hole of the front end cap of the engine housing and a front axial locking member connected to the spindle. A rear end cap fixing mechanism is provided at the rear end of the mandrel. The rear end cap fixing mechanism has a rear positioning kit that mates with the inner hole of the rear end cap of the engine housing and a rear axial locking member connected to the mandrel.

2. The detachable mandrel for fiber-wound engine housing according to claim 1, characterized in that, The front end cap includes a front connector, the front positioning kit includes a front connector positioning sleeve, and the front axial locking component includes a front connector connecting screw, a thrust ball bearing, and a front connector locking nut; the front connector positioning sleeve has an outer positioning surface that mates with the inner hole of the front end cap, the front connector connecting screw passes through the front connector positioning sleeve and is connected to the front connector of the front end cap; the thrust ball bearing is sandwiched between the front connector locking nut and the front connector positioning sleeve; the front connector locking nut is threadedly connected to the mandrel; The rear end cap includes a rear connector, the rear positioning kit includes a rear connector positioning sleeve, and the rear axial locking component includes a rear connector connecting screw, a thrust ball bearing, and a rear connector locking nut. The rear connector positioning sleeve has an outer positioning surface that mates with the inner hole of the rear end cap. The rear connector connecting screw passes through the rear connector positioning sleeve and is connected to the rear connector of the rear end cap. The thrust ball bearing is sandwiched between the rear connector locking nut and the rear connector positioning sleeve. The rear connector locking nut is threadedly connected to the mandrel.

3. The detachable mandrel for fiber-wound engine housing according to claim 1, characterized in that, The mandrel includes a mandrel body and a connecting plate. The connecting plate is disposed on one axial side of the mandrel body and has an axial positioning end face facing the metal frame. The axial positioning end face of the connecting plate abuts against one end of the metal frame.

4. The detachable mandrel for fiber-wound engine housing according to claim 1, characterized in that, At least one of the segmented components is an inward-pointing V-shaped segment, and the radially outer sides of each segmented component together form the continuous support surface.

5. The detachable mandrel for fiber-wound engine housing according to claim 4, characterized in that, The metal frame includes an inward V-shaped structure and an outward V-shaped structure. The two lateral parting surfaces of the inward V-shaped structure are inclined relative to the radial reference surface passing through the circumferential center of the inward V-shaped structure, so that the inward V-shaped structure has a wedge shape in the radial section, and its circumferential width decreases from the outer surface of the cylindrical section towards the mandrel. The outward V-shaped structure segments are arranged adjacent to the inward V-shaped structure segments. The circumferential width of the outward V-shaped structure segments in the radial section increases from the outer surface of the cylindrical section towards the mandrel. The lateral parting surfaces of the adjacent outward V-shaped structure segments and the lateral parting surfaces of the inward V-shaped structure segments cooperate to form an inclined parting interface.

6. The detachable mandrel for a fiber-wound engine housing according to claim 5, characterized in that, The inward-pointing angle of the lateral parting surface of the inward-pointing V-shaped structure relative to the corresponding radial reference surface is 10° to 20°.

7. The detachable mandrel for fiber-wound engine housing according to claim 4, characterized in that, The metal skeleton has an eight-petal structure, of which four petals are inward-facing and the other four petals are outward-facing. Each petal has an axially extending rib on its inner side. The metal skeleton is made of low-alloy structural steel, and the total content of alloying elements in the low-alloy structural steel is no more than 5%.

8. The detachable mandrel for fiber-wound engine housing according to claim 2, characterized in that, The key block includes a first key block and a second key block. The first key block is embedded between the mandrel and the metal frame, and the second key block is embedded between the mandrel and the rear connector positioning sleeve. The two sets of side surfaces of the first key block abut against the keyway wall of the mandrel and the keyway wall of the metal frame, respectively. The two sets of side surfaces of the second key block abut against the keyway wall of the mandrel and the keyway wall of the rear connector positioning sleeve, respectively.

9. The detachable mandrel for a fiber-wound engine housing according to claim 1, characterized in that, The bushing includes an inner hole that mates with the outer periphery of the mandrel, an outer peripheral positioning surface that mates with the inner wall of the metal frame, and an axial end face for the frame clamping nut to press against. The frame clamping nut is threaded to the mandrel, and the frame clamping nut presses against the bushing or the metal frame axially, so that the metal frame, the bushing, the key block, and the mandrel form an axially clamping and circumferentially limiting assembly.

10. A design method for a detachable mandrel for a fiber-wound engine housing, characterized in that, A detachable mandrel for designing a fiber-wound engine housing as described in any one of claims 1-9 comprises the following steps: The initial structural scheme of the spindle and metal frame is determined based on the engine housing parameters. The metal frame includes multiple circumferentially distributed and enclosed segments to form a cylindrical section, and includes at least an inward-pointing segment. The metal frame was disassembled and simulated for verification, confirming that there was no interference in the disassembly path; The stress and strain of the segmented metal skeleton under fiber tension and curing thermal stress were calculated and analyzed using finite element software. The strength and stiffness of the metal skeleton are optimized iteratively using preset stress and strain thresholds; The core mold was fabricated according to the optimized scheme, and the fiber-wound shell was fabricated and tested for bursting.

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