A method for manufacturing a carbon fiber joint for an engine housing

Abstract

This invention discloses a method for manufacturing a carbon fiber joint for engine casings in the field of aerospace engine technology. The method includes: dividing the joint into a planar layer, a side cladding layer, and a bottom cladding layer, wherein the planar layer is the load-bearing core area. During the laying process of the planar layer, vacuum compaction and cold-pressing pre-curing are performed in stages to stabilize the interlayer structure under partially cross-linked resin conditions. Subsequently, the planar layer is embedded into an annular area formed by the side cladding layer and the bottom cladding layer, and a gradient stress transfer structure is constructed through overlapping and continuous adhesive film transition. Finally, surface activation treatment is performed on the bonding area of ​​the embedded part. This invention effectively suppresses debonding and cracking of the composite material due to uneven shrinkage or weak interfaces under high pressure and thermal cycling environments by synergistically controlling the curing internal stress and interlayer bonding quality through segmented pre-curing and gradient interface design, significantly improving the structural integrity and long-term reliability of the joint.

Description

Technical Field

[0001] This invention relates to the field of aerospace engine technology, and in particular to a method for manufacturing a carbon fiber joint for an engine casing. Background Technology

[0002] Existing aero-engine casings are typically formed by integral forging of high-temperature alloys or by welding and machining of separate components. This metallic structure possesses excellent high-temperature strength, creep resistance, and long-term service reliability, meeting the harsh high-temperature, high-pressure, and complex load environments of engines. However, the high density of metallic materials results in a persistently high overall weight of the casing, severely limiting improvements in engine thrust-to-weight ratio and fuel efficiency. While attempts have been made to reduce weight using low-density metals such as titanium alloys, limitations remain in high-temperature performance. Therefore, replacing metallic materials with continuous carbon fiber reinforced resin matrix composites, which possess high specific strength, specific stiffness, and designability, in the manufacture of engine casing joints has become the mainstream technological direction for achieving structural lightweighting. Its core objective is to significantly reduce component weight while maintaining or even improving structural performance.

[0003] To achieve the aforementioned lightweighting goals, the industry has widely explored the use of one-piece molding processes to manufacture composite engine housing joints, in order to reduce the additional weight and stress concentration risks associated with mechanical connections. However, such one-piece molding processes face delamination defects when manufacturing joints with complex curved surfaces, varying thicknesses, and the need to withstand high stress and harsh thermal environments.

[0004] Specifically, during the curing and cooling process, due to differences in the curing shrinkage rate of the resin matrix in different layup areas, insufficient interlayer bonding strength, uneven curing pressure distribution, or insufficient wetting and volatile residues, local or overall delamination and cracking occur between the composite material layers. This delamination defect will seriously weaken the overall load-bearing capacity of the joint and damage the integrity of the structure. Under high pressure, vibration and thermal shock loads inside the engine, it is very easy to cause early failure. Therefore, we propose a manufacturing method for carbon fiber joints for engine housings. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for manufacturing carbon fiber joints for engine housings. By employing segmented pre-curing and gradient interface design, the method effectively suppresses curing delamination and interface debonding, significantly improving the structural integrity and load-bearing durability of the carbon fiber joints under high-pressure and hot-load conditions.

[0006] The objective of this invention is achieved as follows: a method for manufacturing a carbon fiber joint for an engine housing, comprising the following steps:

[0007] S1, Zoned Design: The shell joint is divided into zones, one of which is divided into a flat layer to bear the main load;

[0008] S2, Flat Layer Forming: The prepreg material for the flat layer is laid using a segmented progressive laying process;

[0009] S3, Joint Forming and Laying: Lay the side and bottom wrapping layers in sections, cover with adhesive film, overlap the flat layer at the edges, and reinforce the laying.

[0010] S4, Curing: After curing the semi-finished joint, it is demolded to form the joint body;

[0011] S5, Adding embedded parts: By reserving a pre-formed bonding area in the joint body and simultaneously implementing non-bonding surface protection and bonding surface activation treatment on the metal embedded parts, the embedded parts are installed in a coordinated manner.

[0012] Optionally, in step S1, the process of dividing the region is as follows:

[0013] S11: A temporary resin film is coated on the surface of the mold cavity and then heat-insulated under low pressure and constant temperature conditions;

[0014] S12, records the imprint marks formed by the natural flow of temporary resin;

[0015] S13, based on the geometric shape and distribution density of the imprint marks, the mold cavity is divided into a flat layer, a side layer, and a bottom layer;

[0016] Among them, continuous, dense, and banded trace areas correspond to flat layers, while discontinuous, diffuse, or swirling trace areas correspond to side and bottom cladding layers.

[0017] Optionally, the area is divided into: a flat layer, a side cladding layer, and a bottom cladding layer;

[0018] The divided areas are designated as Area 1, Area 2, Area 3, Area 4, and Area 5.

[0019] Among them, region two is defined as a flat layer;

[0020] Region 1 and Region 5 are defined as side cladding layers;

[0021] Define regions three and four as the lower cladding layers;

[0022] The side cladding and lower cladding are contour structure areas, which are used to seal and shape the flat layer;

[0023] Each region's ply includes a prepreg ply unit, and the ply units are laid sequentially at angles of 45°, -45°, 0°, -45°, 45°, and 90°.

[0024] The layup units are stacked periodically in the thickness direction;

[0025] During the laying process, the first layer of prepreg is vacuum-compacted after being laid, and vacuum compaction is performed every 4 layers.

[0026] Optionally, in step S2, the segmented progressive stress-controlled paving specifically involves:

[0027] S21, Prepreg sheets for each region are prepared based on the part structure;

[0028] S22, based on the layup angle of the prepreg in the flat layer, is cyclically laid and the whole is evenly divided into three layers for laying;

[0029] Specifically: after the first layer is laid, vacuum compaction is performed to form the first precast body and then sealed in a vacuum bag;

[0030] Subsequently, after the second-stage layer is laid, vacuum compaction is performed to form the first preform and then it is sealed in a vacuum bag.

[0031] Finally, after the last layer is laid, vacuum compaction is performed to form a flat precast body, and the ring mold is installed.

[0032] The first preform and the second preform are respectively subjected to cold pressing pre-curing;

[0033] S23, the flat layer precast body with the ring mold installed is transferred to the hot press for curing treatment;

[0034] S24, demold the flat layer and mark the parts according to the mold markings;

[0035] S25, inspect the shape and structure of the flat layer and its dimensional parameters.

[0036] Optionally, in step S2, the cold-pressing pre-curing specifically involves:

[0037] 1) Apply a vacuum pressure less than or equal to -0.095 MPa;

[0038] 2) Heat to 120±5℃ at a rate of 1.0℃ / min to 2.0℃ / min, and set the medium temperature to 125℃;

[0039] Once the fastest heating thermocouple reaches 40°C, pressurization begins, increasing the pressure to 0.6±0.02MPa and maintaining a constant pressure.

[0040] When the slowest heating thermocouple reaches 115℃, it is kept constant for 110-120 minutes.

[0041] Subsequently, the temperature was cooled to below 60°C at a rate of less than or equal to 2.0°C / min, and then the pressure was released. The can was opened when the temperature of the thermocouple that cooled the fastest dropped to below 50°C.

[0042] Optionally, step S3 specifically includes:

[0043] The strategy of prioritizing the laying of the lower cladding layer followed by the laying of the side cladding layer is adopted. The joint sealing surfaces of the lower cladding layer and the side cladding layer are cross-lapped, and the lap joints of the upper and lower layers are staggered along the axial direction.

[0044] First, lay out area three of the lower layer, then lay out area five of the side layer;

[0045] After laying the first layer of prepreg, apply vacuum pressure to the corners of the laying area for local compaction;

[0046] Subsequently, in both Area 4 and Area 1, the strategy of prioritizing the laying of the lower cladding layer and then the side cladding layer was adopted.

[0047] After the tiling is completed, a resin-based adhesive film is applied to the surface of the tiling layers in areas one, three, four, and five to form a sealing layer for interface reinforcement.

[0048] Optionally, the second region is a flat layer. Before filling the flat layer, the surface is mechanically polished, cleaned with anhydrous ethanol, and dried at a constant temperature of 70°C for 2 hours.

[0049] After applying a layer of resin-based adhesive film to the dried ply surface, it is then aligned and embedded into the ply gaps in regions one, three, four, and five using an internal annular reference.

[0050] After embedding, the gaps between the two regions and the surrounding regions are filled and compacted point by point with carbon fiber filaments;

[0051] After filling is completed, the edges of the lower and side cladding layers are subjected to layered flanging treatment;

[0052] Specifically, the flanging operation is carried out layer by layer. For each layer that is folded over, a layer of prepreg is sequentially laid on the surface of the folded layer, and a total of 8 layers of folded overlap are completed.

[0053] The overlapping area and the adhesive film layer in area two form a continuous resin transition structure;

[0054] After the tiling and edge turning are completed, the upper mold is placed on the tiling surface to complete the sealing.

[0055] Optionally, in steps S23 and S4, the curing process specifically includes:

[0056] Transfer the product to a hot press, heat it to 70°C, and keep it at that temperature for 2 hours;

[0057] Then, raise the temperature to 130℃ and keep it warm for 1 hour;

[0058] Then, raise the temperature to 160℃ and keep it warm for 3 hours;

[0059] Finally, raise the temperature to 180℃ and keep it warm for 1.5 hours.

[0060] Optionally, the bonding area of ​​the carbon fiber joint body is pre-reserved with a contoured cavity for accommodating the embedded part, and the non-bonding part of the embedded part is covered with a release material for isolation.

[0061] The bonding surfaces are roughened before being coated with adhesive.

[0062] Place the embedded part into the cavity and apply local pressure. After curing, remove the release material and clean up the excess adhesive.

[0063] The curing process specifically involves placing the connector body in an oven at 50°C for 24 hours.

[0064] After curing, check for delamination and hollow areas in the adhesive layer before proceeding with subsequent machining processes.

[0065] Optionally, after the embedded part is inserted, a clamp is used to apply pressure symmetrically from both ends to check whether the axial positioning of the embedded part and the adhesive layer are evenly bonded.

[0066] The direction of the clamping force corresponds to the boss and cylindrical structure of the embedded part.

[0067] Compared with the prior art, the beneficial effects of the present invention are as follows: through the segmented progressive laying and cold-pressing pre-curing process, vacuum compaction is carried out in stages at intervals of several layers during the laying of the flat layer, and low-temperature curing treatment is carried out at key nodes, which effectively removes interlayer volatiles and air gaps, controls resin flow and cross-linking rate, and releases interlayer shear stress in a gradient manner. This avoids the local debonding and cracking caused by shrinkage differences due to traditional one-time high-temperature and high-pressure curing, and fundamentally solves the risk of delamination failure caused by insufficient wetting, volatile residues and uneven pressure.

[0068] Through the synergistic design of overlapping, continuous transition of adhesive film, and carbon fiber bridging, a three-dimensional gradient transition zone of resin-fiber-adhesive film is formed at the junction of the flat layer and the side / bottom cladding layer, which significantly improves the interlayer bonding strength. At the same time, the bonding surface of the embedded part is activated by plasma and roughened by sandblasting, matched with a special low-shrinkage adhesive and cured at low temperature for a long time, to achieve a strong and tough bond at the metal-composite material interface, and comprehensively improve the structural integrity and durability of the joint under high pressure, thermal cycling and vibration conditions. Attached Figure Description

[0069] 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. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0070] Figure 1 This is a schematic diagram of the manufacturing process of the carbon fiber joint for engine housing provided by the present invention.

[0071] Figure 2 This is a process flow diagram of the carbon fiber joint provided by the present invention.

[0072] Figure 3 This is a schematic diagram of the carbon fiber joint layup area division provided by the present invention.

[0073] Figure 4 This is a schematic diagram of the segmented progressive stress-controlled tiling process provided by the present invention.

[0074] In the diagram: 1. Region 1; 2. Region 2; 3. Region 3; 4. Region 4; 5. Region 5. Detailed Implementation

[0075] 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, and 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.

[0076] like Figures 1 to 4 The method for manufacturing a carbon fiber joint for an engine housing, as shown, includes the following steps:

[0077] S1, Zoned Design: The shell joint is divided into zones, one of which is divided into a flat layer to bear the main load;

[0078] S2, Flat Layer Forming: The prepreg material for the flat layer is laid using a segmented progressive laying process;

[0079] S3, Joint Forming and Laying: Lay the side and bottom wrapping layers in sections, cover with adhesive film, overlap the flat layer at the edges, and reinforce the laying.

[0080] S4, Curing: After curing the semi-finished joint, it is demolded to form the joint body;

[0081] S5, Adding embedded parts: By reserving a pre-formed bonding area in the joint body and simultaneously implementing non-bonding surface protection and bonding surface activation treatment on the metal embedded parts, the embedded parts are installed in a coordinated manner.

[0082] Specifically, in step S1, the process of dividing the region is as follows:

[0083] S11: A temporary resin film is coated on the surface of the mold cavity and then heat-insulated under low pressure and constant temperature conditions;

[0084] S12, records the imprint marks formed by the natural flow of temporary resin;

[0085] S13, based on the geometric shape and distribution density of the imprint marks, the mold cavity is divided into a flat layer, a side layer, and a bottom layer;

[0086] Among them, continuous, dense, and banded trace areas correspond to flat layers, while discontinuous, diffuse, or swirling trace areas correspond to side and bottom cladding layers.

[0087] Furthermore, firstly, the mold of the shell joint is cleaned and a release agent is evenly sprayed. Then, an epoxy resin mixed with fluorescent agent is uniformly scraped along the main axis of the mold to form a continuous film. Subsequently, the mold is placed in a hot press for low-temperature heat preservation and pressure treatment, so that the epoxy resin flows and deposits naturally under the drive of temperature gradient and surface tension without fiber interference, forming visible continuous or discontinuous resin residue traces. The traces are non-randomly distributed, and their morphological characteristics are highly consistent with the actual load transfer path of subsequent lay-ups. Among them, the high-density banded area reflects the main stress flow direction, and the divergent or vortex area reflects the geometric transition and stress release zone.

[0088] Furthermore, the changes in the cross-section of the resin are detected. Based on the direction of the main stress flow, geometric transition and stress release zone of the resin, a closed, fillable ply area for fiber prepreg is drawn. The remaining unmarked trace areas are collectively referred to as non-ply areas. Those that are dotted or low-density distributed are classified as lower cladding, and those that are radial or extend along the edge are classified as side cladding.

[0089] Specifically, the area is divided into: flat layer, side cladding layer, and bottom cladding layer;

[0090] The divided areas are designated as Area 1, Area 2, Area 3, Area 4, and Area 5.

[0091] Among them, region two is defined as a flat layer;

[0092] Region 1 and Region 5 are defined as side cladding layers;

[0093] Define regions three and four as the lower cladding layers;

[0094] The side cladding and lower cladding are contour structure areas, which are used to seal and shape the flat layer.

[0095] Furthermore, in step S1, the shell joint is divided into five distinct functional areas, labeled as one, two, three, four, and five respectively. The flat layer is the core load-bearing area, used to bear the main axial load and internal pressure; areas one and five are side cladding layers, which have a ring structure and whose main function is to suppress radial deformation and form a sealing boundary; areas three and four are lower cladding layers, used to bear bending moment and local impact load and work with the side cladding layers to form a closed-loop seal.

[0096] Furthermore, compared with traditional zoning methods, this invention significantly reduces the average area error and improves the fiber orientation consistency of the layup area during subsequent hot pressing, reducing the rate of decrease in interlayer shear strength. In addition, the equipment used in the above steps are all conventional industrial equipment, all materials can be purchased through open channels, and all parameters used are measurable and reproducible accurate values, completely eliminating the reliance on algorithms and digital models. High-precision and high-consistency zoning can be achieved with only simple measuring tools. It has a low operating threshold, fast response, and extremely low cost. Moreover, the zoning results are highly consistent with the actual layup stress state, significantly improving product quality and production efficiency.

[0097] Specifically, in step S2, the segmented progressive stress-controlled tiling is as follows:

[0098] S21, Prepreg sheets for each region are prepared based on the part structure;

[0099] S22, based on the layup angle of the prepreg in the flat layer, is cyclically laid and the whole is evenly divided into three layers for laying;

[0100] Specifically: after the first layer is laid, vacuum compaction is performed to form the first precast body and then sealed in a vacuum bag;

[0101] Subsequently, after the second-stage layer is laid, vacuum compaction is performed to form the first preform and then it is sealed in a vacuum bag.

[0102] Finally, after the last layer is laid, vacuum compaction is performed to form a flat precast body, and the ring mold is installed.

[0103] The first preform and the second preform are respectively subjected to cold pressing pre-curing;

[0104] S23, the flat layer precast body with the ring mold installed is transferred to the hot press for curing treatment;

[0105] S24, demold the flat layer and mark the parts according to the mold markings;

[0106] S25, inspect the shape and structure of the flat layer and its dimensional parameters.

[0107] Furthermore, the flat layer adopts a segmented progressive stress-controlled laying process, combined with a three-layer progressive laying and cold-press pre-curing system, to achieve gradual control of interlayer stress gradient.

[0108] First, based on the T700 grade carbon fiber unidirectional prepreg (thickness 0.125±0.005mm) and high-temperature epoxy resin, the layup sequence was designed, and the layup angle strictly followed the pattern of [45°, -45°, 0°, -45°, 45°, 90°], with six layers forming one cycle, for a total of 33 cycles;

[0109] The laying process uses a high-precision automatic tape laying machine with a layup angle control accuracy of ±0.5° and an alignment error of less than 1° between the fiber direction and the mold coordinate system.

[0110] After the first section has been laid for 11 cycles, it is immediately sealed in a vacuum bag, a vacuum pressure of less than or equal to -0.095MPa is applied, and it is left to stand for 15 minutes to remove the initial air between the fibers.

[0111] Subsequently, the autoclave heating rate was controlled at 1.5±0.2℃ / min, the medium temperature was set at 125℃, and when the thermocouple reached 40℃ at the highest heating point, a pressure of 0.60±0.02MPa was applied and maintained at a constant pressure. When the thermocouple temperature at the lowest heating point reached 115℃, it was kept at a constant temperature for 115min to ensure that the resin flowed fully and the fiber was wetted. Then, it was cooled to below 60℃ at a rate of 1.8℃ / min. After the temperature dropped below 50℃ at the fastest cooling point, the autoclave was opened and the first preform was taken out.

[0112] This stage involves cold-pressing pre-curing, which partially cross-links the resin without fully curing it. This significantly reduces the accumulation of interlaminar shear stress, suppresses delamination tendency, and effectively avoids fiber buckling and resin extrusion deformation caused by one-time pressure application during full curing.

[0113] After 22 cycles of the second stage, the same vacuum encapsulation and cold-press curing process is repeated to form the second preform. After the 33rd cycle of the final stage, the upper ring mold is precisely pressed onto the layup surface to form a rigid preform, providing a stable geometric base for subsequent structural docking with the side cladding and lower cladding.

[0114] Specifically, each region's layup includes prepreg layup units, which are laid sequentially at angles of 45°, -45°, 0°, -45°, 45°, and 90°.

[0115] The layup units are stacked periodically in the thickness direction;

[0116] During the laying process, the first layer of prepreg is vacuum-compacted after being laid, and vacuum compaction is performed every 4 layers.

[0117] Furthermore, in the multi-layer laying process of carbon fiber composite structure, a cyclic laying method with a specific angle sequence is adopted, and vacuum compaction is carried out after the first layer is laid. The compaction operation is repeated every few layers, which can effectively suppress the accumulation of defects such as fiber slippage, interlayer air gaps and uneven resin distribution.

[0118] The first layer compaction ensures that the prepreg fits fully with the mold surface, laying a flat benchmark for subsequent layers; while periodic intermediate compaction removes trapped air in time before the resin has fully flowed and cured, enhancing interlayer bonding and avoiding the risk of internal stress concentration and delamination due to thickness accumulation.

[0119] Furthermore, this process logic balances the contradiction between resin flowability and layup stability through intermittent vacuum intervention, ensuring both structural density and consistency of mechanical properties, while avoiding efficiency losses and fiber damage caused by excessively frequent operations. Thus, without increasing equipment complexity, it significantly improves the overall molding quality and reliability of large thin-walled irregular parts.

[0120] Specifically, in step S2, cold pressing pre-curing involves:

[0121] 1) Apply a vacuum pressure less than or equal to -0.095 MPa;

[0122] 2) Heat to 120±5℃ at a rate of 1.0℃ / min to 2.0℃ / min, and set the medium temperature to 125℃;

[0123] Once the fastest heating thermocouple reaches 40°C, pressurization begins, increasing the pressure to 0.6±0.02MPa and maintaining a constant pressure.

[0124] When the slowest heating thermocouple reaches 115℃, it is kept constant for 110-120 minutes.

[0125] Subsequently, the temperature was cooled to below 60°C at a rate of less than or equal to 2.0°C / min, and then the pressure was released. The can was opened when the temperature of the thermocouple that cooled the fastest dropped to below 50°C.

[0126] Furthermore, applying a high vacuum can effectively remove residual air between layers and improve fiber wettability; a slow heating rate of 1.0~2.0℃ / min ensures a uniform transition of the internal temperature field of the component, avoiding fiber buckling or interface debonding caused by thermal stress.

[0127] Pressurization (0.6±0.02MPa) is initiated when the fastest heating point reaches 40℃. At this point, the resin has initially softened but has not yet thickened. The pressure can effectively compact the layup and force out excess resin, preventing the formation of resin-rich or resin-poor areas.

[0128] Secondly, after the slowest heating point reaches 115℃, the temperature is held constant for 110~120 minutes to ensure that the resin completes the cross-linking reaction in a highly ordered state of molecular chains, so that the glass transition temperature is fully increased and better mechanical properties and dimensional stability are obtained.

[0129] Finally, the temperature is slowly cooled at a rate of less than or equal to 2.0℃ / min to avoid residual stress concentration caused by excessive temperature difference. The can is opened after the temperature drops to less than or equal to 50℃, which ensures that the substrate has completed the glass transition and is less prone to deformation or surface rebound.

[0130] Specifically, step S3 is as follows:

[0131] The strategy of prioritizing the laying of the lower cladding layer followed by the laying of the side cladding layer is adopted. The joint sealing surfaces of the lower cladding layer and the side cladding layer are cross-lapped, and the lap joints of the upper and lower layers are staggered along the axial direction.

[0132] First, lay out area three of the lower layer, then lay out area five of the side layer;

[0133] After laying the first layer of prepreg, apply vacuum pressure to the corners of the laying area for local compaction;

[0134] Subsequently, in both Area 4 and Area 1, the strategy of prioritizing the laying of the lower cladding layer and then the side cladding layer was adopted.

[0135] After the tiling is completed, a resin-based adhesive film is applied to the surface of the tiling layers in areas one, three, four, and five to form a sealing layer for interface reinforcement.

[0136] Furthermore, the joint forming and laying adopts a coordinated laying strategy of prioritizing the lower cladding layer, followed by the side cladding layers, cross-overlapping, and staggered interfaces. The first laying is done before the prepreg layer in area three (lower cladding layer), with the interlayer laying angle continuing the 90° direction of the last layer of the flat layer, to achieve a smooth stress transition from the flat layer to the lateral load-bearing area. Subsequently, the prepreg layer is laid in area five (side cladding layer), with a laying angle of ±45°, and it cross-overlaps with the lower cladding layer at a 3°~5° angle at the sealing interface, with an overlap width of 12±1mm. The overlap seams of the upper and lower layers are staggered axially by ≥15mm to prevent stress concentration channels from forming. After the first lower cladding layer is laid, a local vacuum is immediately drawn at the conical corner, with a pressure less than or equal to -0.090MPa and an action time of ≥10min. The vacuum adsorption force makes the fibers adhere to the curved surface of the mold, eliminating suspended layers and air pockets. After completing areas three and five, lay out areas four (bottom cladding) and one (side cladding), following the same process as described above to ensure structural symmetry.

[0137] After the cladding is completed, a 0.05mm thick resin-based adhesive film is simultaneously applied to the exposed surfaces of all side and bottom cladding layers to form a dense, non-porous sealing layer. This adhesive film is a solvent-free epoxy resin prepolymer with a viscosity of 800±50cP, a leveling time of 4min at 25℃, and a surface roughness Ra of less than or equal to 1.6μm after curing, which significantly improves the interlayer bonding strength and airtightness.

[0138] Specifically, area two is a flat layer. Before filling the flat layer, the surface is mechanically polished, cleaned with anhydrous ethanol, and dried at a constant temperature of 70°C for 2 hours.

[0139] After applying a layer of resin-based adhesive film to the dried ply surface, it is then aligned and embedded into the ply gaps in regions one, three, four, and five using an internal annular reference.

[0140] After embedding, the gaps between the two regions and the surrounding regions are filled and compacted point by point with carbon fiber filaments;

[0141] After filling is completed, the edges of the lower and side cladding layers are subjected to layered flanging treatment;

[0142] Specifically, the flanging operation is carried out layer by layer. For each layer that is folded over, a layer of prepreg is sequentially laid on the surface of the folded layer, and a total of 8 layers of folded overlap are completed.

[0143] The overlapping area and the adhesive film layer in area two form a continuous resin transition structure to achieve stress gradient transition.

[0144] After the tiling and edge turning are completed, the upper mold is placed on the tiling surface to complete the sealing.

[0145] Furthermore, before embedding the planar layer, its surface is mechanically activated: sandpaper is used to uniformly grind along the axial direction to remove the release film residue and oxide layer on the surface, and the roughness Ra is increased from the original 0.8μm to 4.2±0.3μm. Then, it is ultrasonically washed three times with anhydrous ethanol for 15 minutes each time, and then placed in a constant temperature oven at 70±2℃ for 2 hours to ensure that the residual moisture content is less than 50ppm.

[0146] After drying, a layer of resin-based adhesive film is coated on the surface of the flat layer as an interface transition layer. The preform is then aligned and embedded into the annular space consisting of regions one, three, four, and five, using the inner ring of the mold as a reference. After embedding, the peripheral gap is measured with a laser rangefinder, and the maximum gap does not exceed 0.5 mm. T700 carbon fiber filaments are then filled point by point along this gap, and pressure is applied in the circumferential direction using a carbon fiber pressure roller to compact the carbon filaments and fuse them with the adhesive film, forming a fiber bridging layer with a bridging length of up to 8 mm, which significantly enhances the interlaminar shear strength between the flat layer and the annular covering layer. Subsequently, a layered folding operation is performed: using the outermost layer of the flat layer as the base, the edges of the side covering layer and the lower covering layer are folded layer by layer from bottom to top. After each fold, a layer of prepreg at the same angle as the parent layer is immediately laid on the folded surface, completing a total of 8 layers of folding overlap. The flange stress is continuously transitioned through the adhesive film: the adhesive film layer in region 2 forms a continuous resin gradient network with the first flange adhesive film, the second flange adhesive film, and so on up to the eighth flange adhesive film, which fundamentally avoids the interface debonding caused by the "stress peak" that occurs in traditional non-overlapping structures under high loads.

[0147] Specifically, in steps S23 and S4, the curing process is as follows:

[0148] Transfer the product to a hot press, heat it to 70°C, and keep it at that temperature for 2 hours;

[0149] Then, raise the temperature to 130℃ and keep it warm for 1 hour;

[0150] Then, raise the temperature to 160℃ and keep it warm for 3 hours;

[0151] Finally, raise the temperature to 180℃ and keep it warm for 1.5 hours.

[0152] Furthermore, the temperature was first increased to 70℃ at 1.2℃ / min and held for 2 hours to allow the residual solvent and low molecular weight components to evaporate; then, the temperature was increased to 130℃ at 1.0℃ / min and held for 1 hour to trigger the cyclization reaction of the resin backbone; next, the temperature was increased to 160℃ at 0.8℃ / min and held for 3 hours to complete the core crosslinking reaction. At this point, the resin viscosity dropped below 10^3 Pa·s, the molecular chains were fully entangled, and the glass transition point increased significantly; finally, the temperature was increased to 180℃ at 0.5℃ / min and held for 1.5 hours to achieve complete curing, ensuring that the crosslinking density reached above 2.8×10⁻³ mol / cm³ and the thermal decomposition temperature exceeded 360℃.

[0153] Furthermore, a uniform pressure of 0.5±0.05MPa is applied throughout the curing process. The pressure is transmitted through a rigid pressure plate to ensure isotropic compression and avoid in-plane warping.

[0154] Specifically, the bonding area of ​​the carbon fiber joint body has a pre-reserved contoured cavity for accommodating the embedded part, and the non-bonding parts of the embedded part are covered with release material for isolation.

[0155] The bonding surfaces are roughened before being coated with adhesive.

[0156] Place the embedded part into the cavity and apply local pressure. After curing, remove the release material and clean up the excess adhesive.

[0157] The curing process involves placing the connector body in an oven at 50°C for 24 hours.

[0158] After curing, check for delamination and hollow areas in the adhesive layer before proceeding with subsequent machining processes.

[0159] Specifically, after the embedded part is placed, a clamp is used to apply pressure symmetrically from both ends to check whether the axial positioning of the embedded part and the adhesive layer are evenly bonded.

[0160] The direction of the clamping force corresponds to the boss and cylindrical structure of the embedded part.

[0161] Furthermore, after curing, the joint body has a pre-reserved contour-shaped cavity whose shape precisely corresponds to the shape of the stainless steel embedded part. The inner wall is treated with nitrogen plasma etching to increase the surface energy to over 52mN / m. After ultrasonic cleaning with Grade A acetone for 30 minutes, it is dried and then uniformly coated with a self-developed two-component epoxy adhesive (model JY-805). Its shear strength is ≥35MPa, the applicable temperature is -55℃ to +150℃, and the curing time is 80min±5min. The embedded part is made of 316L stainless steel. Its non-bonding surfaces (such as the internal thread surface and the back of the mounting flange) are covered with a 0.1mm thick polytetrafluoroethylene release cloth. The edges of the release cloth are sealed with high-temperature tape to ensure that the adhesive only acts on the target bonding surface.

[0162] The bonding surface is sandblasted to form uniform micro-pits with an average pit depth of 6-8 μm, increasing the specific surface area by 3.2 times and providing mechanical anchoring for the adhesive layer. After the embedded part is placed into the cavity, a customized rigid clamp is used to apply pressure symmetrically from both ends. The clamping force is strictly along the axis of the embedded part, acting on its boss surface and cylindrical end, and static pressure is maintained for 10 minutes to expel air from the adhesive layer.

[0163] The joint was then placed in a constant temperature oven and heated to 50℃ at a rate of 0.3℃ / min, and held for 24 hours to allow the adhesive to fully cross-link. After demolding, ultrasonic C-scan was used to detect adhesive layer voids, with a threshold set at 4.5dB attenuation; any signal exceeding this value was considered a defect. A laser rangefinder was then used to check the axial positioning deviation of the embedded parts, controlling it within ±0.1mm. Finally, an axial tensile test was performed on the threaded sleeve: a 270kN tensile testing machine was used. When the load reached 258kN, the specimen did not experience fiber breakage, debonding, or abnormal noise, and the load-bearing capacity met the design value.

[0164] In summary, this method constitutes a closed-loop technical system comprised of three elements: segmented pre-curing of the layup, gradient stress transition through overlapping seams, and activation treatment of the embedded parts and substrate. Segmented pre-curing significantly reduces internal stress within the layup, overlapping seams achieve longitudinal gradient load transfer, and activation of the embedded parts interface ensures long-term stable bonding of the metal-organic interface. Compared to traditional metal joints, the carbon fiber joints manufactured using this method are lighter, have increased axial load-bearing capacity, achieve an airtightness compliance pressure of 12.3 MPa, a burst pressure of 18.1 MPa, and show no debonding or delamination after 50 thermal cycles at -40℃ to 120℃.

[0165] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for manufacturing a carbon fiber joint for an engine housing, characterized in that, Includes the following steps: S1, Zoned Design: The shell joint is divided into zones, one of which is divided into a flat layer to bear the main load; S2, Flat Layer Forming: A segmented, progressive laying process is used for laying the prepreg in the flat layer; the segmented, progressive stress-controlled laying process specifically involves: S21, Prepreg sheets for each region are prepared based on the part structure; S22, based on the layup angle of the prepreg in the flat layer, is cyclically laid and the whole is evenly divided into three layers for laying; Specifically: after the first layer is laid, vacuum compaction is performed to form the first precast body and then sealed in a vacuum bag; Subsequently, after the second-stage layer is laid, vacuum compaction is performed to form the first preform and then it is sealed in a vacuum bag. Finally, after the last layer is laid, vacuum compaction is performed to form a flat precast body, and the ring mold is installed. The first preform and the second preform are respectively subjected to cold pressing pre-curing; S23, the flat layer precast body with the ring mold installed is transferred to the hot press for curing treatment; S24, demold the flat layer and mark the parts according to the mold markings; S25, inspect the shape and structure of the flat layer and its dimensional parameters; S3, Joint Forming and Laying: Lay the side and bottom wrapping layers in sections, cover with adhesive film, overlap the flat layer at the edges, and reinforce the laying. S4, Curing: After curing the semi-finished joint, it is demolded to form the joint body; S5, Adding embedded parts: By reserving a pre-formed bonding area in the joint body and simultaneously implementing non-bonding surface protection and bonding surface activation treatment on the metal embedded parts, the embedded parts are installed in a coordinated manner.

2. The method for manufacturing a carbon fiber joint for an engine housing according to claim 1, characterized in that: In step S1, the process of dividing the region is as follows: S11: A temporary resin film is coated on the surface of the mold cavity and then heat-insulated under low pressure and constant temperature conditions; S12, records the imprint marks formed by the natural flow of temporary resin; S13, based on the geometric shape and distribution density of the imprint marks, the mold cavity is divided into a flat layer, a side layer, and a bottom layer; Among them, continuous, dense, and banded trace areas correspond to flat layers, while discontinuous, diffuse, or swirling trace areas correspond to side and bottom cladding layers.

3. The method for manufacturing a carbon fiber joint for an engine housing according to claim 2, characterized in that: The area is divided into: a flat layer, a side cladding layer, and a bottom cladding layer; The divided areas are designated as Area 1, Area 2, Area 3, Area 4, and Area 5. Among them, region two is defined as a flat layer; Region 1 and Region 5 are defined as side cladding layers; Define regions three and four as the lower cladding layers; The side cladding and lower cladding are contour structure areas, which are used to seal and shape the flat layer; Each region's ply includes a prepreg ply unit, and the ply units are laid sequentially at angles of 45°, -45°, 0°, -45°, 45°, and 90°. The layup units are stacked periodically in the thickness direction; During the laying process, the first layer of prepreg is vacuum-compacted after being laid, and vacuum compaction is performed every 4 layers.

4. The method for manufacturing a carbon fiber joint for an engine housing according to claim 1, characterized in that: In step S2, the cold-pressing pre-curing specifically involves: 1) Apply a vacuum pressure less than or equal to -0.095 MPa; 2) Heat to 120±5℃ at a rate of 1.0℃ / min to 2.0℃ / min, and set the medium temperature to 125℃; Once the fastest heating thermocouple reaches 40°C, pressurization begins, increasing the pressure to 0.6±0.02MPa and maintaining a constant pressure. When the slowest heating thermocouple reaches 115℃, it is kept constant for 110-120 minutes. Subsequently, the temperature was cooled to below 60°C at a rate of less than or equal to 2.0°C / min, and then the pressure was released. The can was opened when the temperature of the thermocouple that cooled the fastest dropped to below 50°C.

5. A method for manufacturing a carbon fiber joint for an engine housing according to claim 3, characterized in that: Step S3 is as follows: The strategy of prioritizing the laying of the lower cladding layer followed by the laying of the side cladding layer is adopted. The joint sealing surfaces of the lower cladding layer and the side cladding layer are cross-lapped, and the lap joints of the upper and lower layers are staggered along the axial direction. First, lay out area three of the lower layer, then lay out area five of the side layer; After laying the first layer of prepreg, apply vacuum pressure to the corners of the laying area for local compaction; Subsequently, in both Area 4 and Area 1, the strategy of prioritizing the laying of the lower cladding layer and then the side cladding layer was adopted. After the tiling is completed, a resin-based adhesive film is applied to the surface of the tiling layers in areas one, three, four, and five to form a sealing layer for interface reinforcement.

6. The method for manufacturing a carbon fiber joint for an engine housing according to claim 5, characterized in that: The second area is a flat layer. Before filling the flat layer, the surface is mechanically polished, cleaned with anhydrous ethanol, and dried at a constant temperature of 70°C for 2 hours. After applying a layer of resin-based adhesive film to the dried ply surface, it is then aligned and embedded into the ply gaps in regions one, three, four, and five using an internal annular reference. After embedding, the gaps between the two regions and the surrounding regions are filled and compacted point by point with carbon fiber filaments; After filling is completed, the edges of the lower and side cladding layers are subjected to layered flanging treatment; Specifically, the flanging operation is carried out layer by layer. For each layer that is folded over, a layer of prepreg is sequentially laid on the surface of the folded layer, and a total of 8 layers of folded overlap are completed. The overlapping area and the adhesive film layer in area two form a continuous resin transition structure; After the tiling and edge turning are completed, the upper mold is placed on the tiling surface to complete the sealing.

7. A method for manufacturing a carbon fiber joint for an engine housing according to claim 1, characterized in that: In steps S23 and S4, the curing process specifically includes: Transfer the product to a hot press, heat it to 70°C, and keep it at that temperature for 2 hours; Then, raise the temperature to 130℃ and keep it warm for 1 hour; Then, raise the temperature to 160℃ and keep it warm for 3 hours; Finally, raise the temperature to 180℃ and keep it warm for 1.5 hours.

8. A method for manufacturing a carbon fiber joint for an engine housing according to claim 1, characterized in that: The bonding area of ​​the connector body has a pre-reserved contoured cavity for accommodating the embedded part, and the non-bonding parts of the embedded part are covered with release material for isolation. The bonding surfaces are roughened before being coated with adhesive. Place the embedded part into the cavity and apply local pressure. After curing, remove the release material and clean up the excess adhesive. The curing process specifically involves placing the connector body in an oven at 50°C for 24 hours. After curing, check for delamination and hollow areas in the adhesive layer before proceeding with subsequent machining processes.

9. A method for manufacturing a carbon fiber joint for an engine housing according to claim 8, characterized in that: After the embedded parts are inserted, clamps are used to apply pressure symmetrically from both ends to check whether the axial positioning of the embedded parts and the adhesive layer are evenly bonded. The direction of the clamping force corresponds to the boss and cylindrical structure of the embedded part.

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