A method for manufacturing a non-uniform diameter, thick, closed-loop tubular carbon fiber beam

Abstract

This invention discloses a method for manufacturing a non-uniform diameter, thick, closed-type tubular carbon fiber beam in the field of carbon fiber beam technology for wind tunnel blades. The method includes: S1, disassembling the carbon fiber beam structure and preparing a specially designed mold with corresponding cavities; S2, laying a carbon fiber preform on the mold; S3, assembling the preform after demolding and fixing the mold; S4, setting vacuum bags and placing vacuum nozzles on the inner and outer sides of the assembled mold; S5, placing the mold in a thermosetting device and using a gradient curing process with vacuum pressure for curing; S6, demolding after cooling. This invention, by employing co-curing in a thermosetting tank, results in excellent overall performance of the carbon fiber beam, eliminating the need for additional adhesives and secondary bonding steps, reducing air bubbles and defects. Simultaneously, dividing the carbon fiber beam into three parts disperses the thickness, improving the laying quality and efficiency, increasing the bonding surface of the carbon fiber beam, and enhancing the bonding strength.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber beams for wind tunnel blades, and particularly to a method for manufacturing a non-uniform diameter, thick, closed-type tubular carbon fiber beam. Background Technology

[0002] With advancements in wind tunnel blade technology, the structural design of carbon fiber beams is becoming increasingly diversified. Compared to traditional equal-diameter square tubular structures, non-equal-diameter closed-loop carbon fiber square tubular beams have attracted significant attention due to their superior configuration fit and load-bearing capacity. However, currently, these beams are primarily manufactured using a monolithic molding process, which faces numerous challenges in actual production: not only are there difficulties in demolding and complex processes, but also long production cycles and high costs. Furthermore, this process places extremely high demands on molding technology and specialized tooling equipment, all of which restrict its large-scale application.

[0003] According to CN110654039B, a method for manufacturing a non-uniform diameter closed-type square tubular carbon fiber beam structure for unmanned aerial vehicles is disclosed, including the following steps: 1) processing an upper female mold and a lower female mold; 2) processing an upper beam using the upper female mold; 3) processing a lower beam using the lower female mold; 4) gluing the upper beam and the lower beam together using an adhesive bonding fixture; 5) removing the adhesive bonding fixture to obtain the desired non-uniform diameter closed-type square tubular carbon fiber beam.

[0004] However, this method is only suitable for carbon fiber parts with small thickness. For tubular beams with large thickness, the secondary bonding surface is difficult to be compressed, and the bonding surface is a single-sided bonding with a small bonding area and poor overall performance. Therefore, we propose a manufacturing method for non-uniform diameter, large-thickness closed tubular carbon fiber beams. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for manufacturing a non-uniform diameter, thick, closed-type tubular carbon fiber beam. The method divides the carbon fiber beam into three parts to distribute the thickness, improving the laying quality and efficiency, increasing the bonding surface of the carbon fiber beam, and enhancing the bonding strength. Furthermore, the method utilizes autoclave co-curing to solve problems such as poor secondary bonding quality of the carbon fiber beam and poor compaction effect of the thick beam.

[0006] The objective of this invention is achieved as follows: a method for manufacturing a non-uniform diameter, thick, closed-loop tubular carbon fiber beam, comprising the following steps:

[0007] S1, the structure of the carbon fiber beam is decomposed and optimized, and a special mold with corresponding cavity is prepared based on the decomposed structure;

[0008] S2, prefabricated carbon fiber beams are laid on a special mold;

[0009] S3, demold the carbon fiber beam preform, assemble the preform in the second lower beam mold, and then fix it in place;

[0010] S4, Vacuum bags are set on the inner and outer sides of the combined mold to form inner and outer vacuum bags, and vacuum nozzles are placed there;

[0011] S5, the combined mold with the vacuum bag is placed in the hot press device, and the gradient curing process is used to perform vacuuming and pressure curing.

[0012] S6. After the mold cools down, remove the mold and demold the product.

[0013] Optionally, in step S1, the carbon fiber beam is divided into an upper beam, a first lower beam, and a second lower beam;

[0014] Molds with corresponding cavities are prepared based on the upper beam, the first lower beam, and the second lower beam;

[0015] The second lower beam mold serves as both a laying mold and a curing mold.

[0016] Optionally, the specially designed mold assembly constitutes the upper beam cavity and the first lower beam cavity of the carbon fiber beam; the second lower beam mold is a spliced ​​structure.

[0017] Optionally, the specific process of step S2 is as follows:

[0018] Clean the surface of each mold cavity and set demolding aids. According to the design requirements for thickness and laying angle, lay carbon fiber prepreg on the inner surface of the corresponding cavity mold. After the first layer is laid, make a vacuum bag for pre-extraction and compaction.

[0019] Optionally, the pre-compression of the vacuum bag is specifically:

[0020] The pre-evacuation time is 15-20 minutes. The pre-evacuation time is calculated from the point when the vacuum degree inside the vacuum bag is ≤-0.085MPa. Thereafter, pre-evacuation is performed once every 10 layers, and cold pressing is performed once every 30 layers.

[0021] The specific cold pressing parameters are: 0.6 MPa, temperature 60℃, and time 1 hour;

[0022] After each precast component is laid, the prepreg is cold-pressed to compact it.

[0023] Optionally, the process of step S3 is as follows:

[0024] First, demold the completed upper beam precast body and the first lower beam precast body, and transfer them into the second lower beam mold. Fill the R-corner positions on both sides with prepreg, cover the mold with the upper cover plate, and fix the mold in place.

[0025] Optionally, the specific process of step 4 is as follows:

[0026] First, the tubular vacuum bag and breathable felt are placed inside the tubular isolation membrane;

[0027] The tubular isolation membrane is passed from the inner cavity of the carbon fiber beam to the other side;

[0028] Then, a vacuum bag is placed on the outside of the first lower beam mold. The vacuum bag has 6 vacuum nozzles inside and is connected to the inner bag by putty strips to form inner and outer vacuum bags.

[0029] Optionally, the length of the breathable felt is greater than the length of the carbon fiber beam, the length of the tubular isolation membrane is greater than the length of the breathable felt, and the length of the tubular vacuum bag exceeds the carbon fiber beam mold by 50cm.

[0030] The vacuum bag has a tubular isolation membrane with a width greater than the maximum inner diameter of its inner cavity.

[0031] The breathable felt is divided into sections on all four sides to form an inner bag.

[0032] Optionally, in step S5, the gradient curing process specifically includes:

[0033] S51, transfer the mold to the autoclave platform, check whether the vacuum bag meets the standard, and only after the vacuum test meets the standard can the heating program be started;

[0034] S52, the autoclave is heated to 80°C at a rate of 1°C / min;

[0035] S53, maintain 80°C for heat preservation and pressure maintenance for 2 hours ± 10 minutes;

[0036] S54, the autoclave is subjected to a global pressure of 0.6MPa, and when the temperature is raised to 130℃, it is held for 3h±10min;

[0037] S55, turn off the heating and allow it to cool naturally to below 60℃.

[0038] Optionally, the specific steps for detecting whether the vacuum bag meets the standards are:

[0039] Transfer the mold to the autoclave platform, connect it to the vacuum system, apply a vacuum pressure below -0.085MPa, and apply an air pressure of 0.6MPa. Maintain this pressure for at least 5 minutes without leakage, then turn off the vacuum system. Within 5 minutes, the vacuum gauge reading should not drop by more than 0.02MPa.

[0040] Otherwise, the vacuum bags should be inspected and repaired. If they do not meet the standards, the vacuum bags should be resealed.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows: The thick closed tubular carbon fiber beam manufactured by the present invention adopts co-curing molding, resulting in excellent overall performance and high interface strength; no additional adhesives and secondary bonding steps are required, and the overall structure is cured under the same conditions, ensuring the consistency of each part; at the same time, the carbon fiber beam is divided into three parts to disperse the thickness, improve the laying quality and laying efficiency, increase the bonding surface of the carbon fiber beam, and improve the bonding strength. Attached Figure Description

[0042] 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.

[0043] Figure 1 This is a schematic diagram of the manufacturing process of a non-uniform diameter, thick, closed tubular carbon fiber beam provided by the present invention.

[0044] Figure 2 This is a schematic diagram of the carbon fiber beam structure provided by the present invention.

[0045] Figure 3 This is a schematic diagram of the cross-section of the carbon fiber beam provided by the present invention.

[0046] Figure 4 This is a schematic diagram of the upper beam mold and the upper beam precast body provided by the present invention.

[0047] Figure 5 This is a schematic diagram of the second lower beam mold and the second lower beam prefabricated body structure provided by the present invention.

[0048] Figure 6 This is a schematic diagram of the mold closing structure provided by the present invention. Detailed Implementation

[0049] 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.

[0050] like Figures 1 to 5 The invention illustrates a method for manufacturing a non-uniform diameter, thick, closed-loop tubular carbon fiber beam.

[0051] Includes the following steps:

[0052] S1, the structure of the carbon fiber beam is decomposed and optimized, and a special mold with corresponding cavity is prepared based on the decomposed structure;

[0053] S2, prefabricated carbon fiber beams are laid on a special mold;

[0054] S3, demold the carbon fiber beam precast body, assemble the precast body in the lower beam mold, and then fix it by mold closing;

[0055] S4, Vacuum bags are set on the inner and outer sides of the combined mold to form inner and outer vacuum bags, and vacuum nozzles are placed there;

[0056] S5, the combined mold with the vacuum bag is placed in the hot press device, and the gradient curing process is used to perform vacuuming and pressure curing.

[0057] S6. After the mold cools down, remove the mold and demold the product.

[0058] It should be noted that this invention addresses the manufacturing challenge of thick, non-uniform diameter closed-cell carbon fiber beams by proposing an innovative split-component co-curing molding method.

[0059] First, by breaking the carbon fiber beam structure into multiple prefabricated units, adopting a zoned heat-conducting mold design and inner and outer double-layer vacuum bag packaging technology, combined with a zoned gradient curing process with differentiated temperature and pressure control, the technical bottlenecks such as difficult demolding and insufficient secondary bonding strength of the traditional integral molding process are effectively solved.

[0060] This method abandons the stringent requirements of traditional adhesive bonding processes for adhesives and surface treatments. Through the synergistic effect of separate prefabrication and overall co-curing, it improves the overall performance of carbon fiber beams and simplifies the process route.

[0061] Compared with existing technologies, this invention improves the compaction quality of thick-walled composite materials and reduces process complexity while ensuring the integrity of the structure, providing a practical solution for the low-cost and efficient manufacturing of large irregular carbon fiber components.

[0062] Specifically, in step S1, the carbon fiber beam is divided into an upper beam, a first lower beam, and a second lower beam;

[0063] Molds with corresponding cavities are prepared based on the upper beam, the first lower beam, and the second lower beam;

[0064] The second lower beam mold serves as both a laying mold and a curing mold.

[0065] Furthermore, by designing the second lower beam mold as a composite mold that combines laying and forming functions, firstly, when used as a laying mold, its cavity structure can precisely guide the laying direction and angle of the fiber prepreg, ensuring that the shape and fiber orientation of the preform meet the design requirements.

[0066] When used as a molding die, it can directly participate in the subsequent assembly and curing process, avoiding the risk of fiber misalignment or deformation caused by preform transfer in traditional processes. This not only simplifies the process flow but also reduces the number of molds and process changeover time. More importantly, it ensures the dimensional stability of the preform throughout the entire process from laying to curing. Especially for carbon fiber beams with large thickness and complex shapes, it can effectively control manufacturing tolerances and improve product consistency and reliability.

[0067] Specifically, the specially designed molds are combined to form the upper beam cavity and the first lower beam cavity of the carbon fiber beam; the second lower beam mold is a spliced ​​structure.

[0068] Specifically, the process of step S2 is as follows:

[0069] Clean the surfaces of each mold cavity and apply demolding aids accordingly. Lay carbon fiber prepreg on the inner surface of the corresponding mold cavity according to the design requirements for thickness and laying angle. After the first layer is laid, make a vacuum bag for pre-extraction and compaction.

[0070] Among them, the upper beam and the first lower beam molds are covered with release cloth, and the cavities of the other molds are coated with release agent.

[0071] The vacuum bag pre-compression is specifically as follows:

[0072] The pre-evacuation time is 15-20 minutes. The pre-evacuation time is calculated from the point when the vacuum degree inside the vacuum bag is ≤-0.085MPa. Thereafter, pre-evacuation is performed once every 10 layers, and cold pressing is performed once every 30 layers.

[0073] The specific cold pressing parameters are: 0.6 MPa, temperature 60℃, and time 1 hour;

[0074] After each precast component is laid, the prepreg is cold-pressed to compact it.

[0075] Furthermore, the quality of carbon fiber preforms is significantly improved by using a combination of "pre-vacuuming + cold pressing" process. Pre-vacuuming quickly removes air between the prepreg and the mold, ensuring tight bonding between layers and reducing air bubbles and pores.

[0076] Pre-extraction every 10 layers can remove gas and volatiles trapped during the laying process in real time, preventing the accumulation of voids between layers;

[0077] The 30-layer cold pressing method utilizes the synergy of temperature and pressure to improve the density of the precast structure.

[0078] Specifically, the process of step S3 is as follows:

[0079] First, demold the completed upper beam precast body and the first lower beam precast body, and transfer them into the second lower beam mold. Fill the R-corner positions on both sides with prepreg, cover the mold with the upper cover plate, and fix the mold in place.

[0080] Furthermore, prepreg is used to locally supplement the R-corner to ensure continuous fiber laying in this critical area, guarantee the integrity of the load transfer path, effectively avoid stress concentration caused by fiber discontinuity or excessive adhesive, thereby enhancing the compression, shear and impact resistance of the structural corner, fundamentally preventing failure modes such as delamination and cracking that are prone to occur in this area under stress, while improving the dimensional accuracy and surface quality of the R-corner area.

[0081] Specifically, the process of step 4 is as follows:

[0082] First, the tubular vacuum bag and breathable felt are placed inside the tubular isolation membrane;

[0083] The tubular isolation membrane is passed from the inner cavity of the carbon fiber beam to the other side;

[0084] Then, a vacuum bag is placed on the outside of the first lower beam mold. The vacuum bag has 6 vacuum nozzles inside and is connected to the inner bag by putty strips to form inner and outer vacuum bags.

[0085] Specifically, the length of the breathable felt is greater than the length of the carbon fiber beam, the length of the tubular isolation membrane is greater than the length of the breathable felt, and the length of the tubular vacuum bag exceeds the carbon fiber beam mold by 50cm.

[0086] The vacuum bag has a tubular isolation membrane with a width greater than the maximum inner diameter of its inner cavity.

[0087] The breathable felt is divided into sections on all four sides to form an inner bag.

[0088] Furthermore, the internal tubular isolation membrane and vacuum bag structure can precisely wrap the inner cavity of the beam, forming a complete vacuum seal. This ensures uniform and continuous compaction and degassing of the prepreg from the inside, effectively guaranteeing the surface quality of the inner cavity. The external vacuum bag integrates six vacuum nozzles, which work in conjunction with the inner bag to form a stable negative pressure field. This not only improves the redundancy and pumping efficiency of the vacuum system and ensures uniform pressure transmission, preventing uneven pressure from causing wrinkles or insufficient resin, but also allows the resin to fully flow and impregnate the fibers through the synergistic effect of the internal and external pressure differences, thereby improving the mechanical properties and structural stability of the composite beam.

[0089] Specifically, in step S5, the gradient curing process is as follows:

[0090] S51, transfer the mold to the autoclave platform, check whether the vacuum bag meets the standard, and only after the vacuum test meets the standard can the heating program be started;

[0091] S52, the autoclave is heated to 80°C at a rate of 1°C / min;

[0092] S53, maintain 80°C for heat preservation and pressure maintenance for 2 hours ± 10 minutes;

[0093] S54, the autoclave is subjected to a global pressure of 0.6MPa, and when the temperature is raised to 130℃, it is held for 3h±10min;

[0094] S55, turn off the heating and allow it to cool naturally to below 60℃.

[0095] Furthermore, this invention achieves precise thermal and mechanical synergistic control in different regions of carbon fiber beams through a gradient curing process;

[0096] Furthermore, by dynamically adjusting temperature and pressure parameters, the resin system can complete the impregnation, flow, and curing process under optimal conditions, ensuring the overall structural density while avoiding stress concentration and deformation problems caused by traditional curing methods, thus significantly improving the overall performance and dimensional stability of composite material components.

[0097] Specifically, the process of testing whether vacuum bags meet the standards is as follows:

[0098] Transfer the mold to the autoclave platform, connect it to the vacuum system, apply a vacuum pressure below -0.085MPa, and apply an air pressure of 0.6MPa. Maintain this pressure for at least 5 minutes without leakage, then turn off the vacuum system. Within 5 minutes, the vacuum gauge reading should not drop by more than 0.02MPa.

[0099] Otherwise, the vacuum bags should be inspected and repaired. If they do not meet the standards, the vacuum bags should be resealed.

[0100] In summary, the thick, closed-loop tubular carbon fiber beam manufactured by this invention is produced through co-curing, resulting in excellent overall performance and high interfacial strength. It eliminates the need for additional adhesives and secondary curing steps, ensuring consistency across all parts as the entire structure is cured under identical conditions. The autoclave co-curing process allows for better control of resin flow and fiber impregnation, reducing bubbles and defects. Furthermore, dividing the carbon fiber beam into three parts disperses the thickness, improving laying quality and efficiency, increasing the bonding surface area, and enhancing bond strength.

[0101] 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 of manufacturing a non-equal-diameter, large-thickness, closed-type tubular carbon fiber beam, characterized by, The method comprises the following steps: S1, the structure of the carbon fiber beam is split and optimized, and a special mold corresponding to the split structure is prepared; in step S1, the carbon fiber beam is divided into an upper beam, a first lower beam and a second lower beam; a mold corresponding to the upper beam, the first lower beam and the second lower beam is prepared respectively; the second lower beam mold is used as a laying mold and also as a curing mold; S2, the preforms of the carbon fiber beam are laid on the special mold respectively; the special mold is combined to form the upper beam cavity and the first lower beam cavity of the carbon fiber beam; the second lower beam mold is a splicing structure; S3, the carbon fiber beam preforms are demolded, combined in the lower beam mold, and then fixed by mold closing; S4, vacuum bags are arranged on the inner side and the outer side of the combined mold respectively to form inner and outer vacuum bags, and a vacuum nozzle is placed; the specific process is as follows: First, the tubular vacuum bag and the air-permeable felt are sleeved in the tubular isolation film; The tubular isolation film is passed from the inner cavity of the carbon fiber beam to the other side; Then, a vacuum bag is sleeved on the outer side of the first lower beam mold, six vacuum nozzles are arranged inside the vacuum bag, and the inner and outer vacuum bags are connected by putty strips; The length of the air-permeable felt is greater than the length of the carbon fiber beam, the length of the tubular isolation film is greater than the length of the air-permeable felt, and the length of the tubular vacuum bag exceeds the length of the carbon fiber beam mold by 50 cm; The width of the vacuum bag and the tubular isolation film is greater than the maximum inner diameter of the inner cavity; The air-permeable felt is divided into blocks on four sides to form an inner bag; S5, the combined mold with the sleeved vacuum bag is placed in a hot pressing device, a gradient curing process is adopted, and vacuumizing and pressure curing are performed; the gradient curing process is specifically as follows: S51, the mold is transported to the platform of the hot pressing tank, it is detected whether the vacuum bag meets the standard, and only when the vacuum detection meets the standard, the temperature rising program can be started; S52, the hot pressing tank is heated to 80°C at a rate of 1°C / min; S53, keep 80°C for 2h±10min; S54, the hot pressing tank applies a pressure of 0.6MPa, and when the temperature rises to 130°C, keep for 3h±10min; S55, turn off the heating, and naturally cool down to below 60°C; S6, after the mold is cooled, the mold is disassembled, and the product is demolded.

2. A method of manufacturing a non-equal-diameter, large-thickness, closed-type tubular carbon fiber beam according to claim 1, characterized by: The specific process of step S2 is as follows: Clean the surfaces of each mold cavity, and arrange demolding auxiliary materials respectively, lay carbon fiber prepreg on the inner surfaces of the corresponding cavity molds according to the designed thickness and laying angle, after the first layer of laying is completed, make a vacuum bag for pre-vacuumizing and compacting.

3. A method of manufacturing a non-equal-diameter, large-thickness, closed-type tubular carbon fiber beam according to claim 2, characterized by: The vacuum bag pre-compaction is specifically as follows: The pre-vacuumizing time is 15-20min, the pre-vacuumizing is started when the vacuum degree in the vacuum bag is less than or equal to-0.085MPa, and then pre-vacuumizing is performed every 10 layers, and cold pressing is performed every 30 layers; The cold pressing parameters are specifically as follows: 0.6Mpa, temperature 60°C, and time 1h; After the laying of each preform is completed, the prepreg is cold-pressed and compacted.

4. The method of manufacturing a non-equal- diameter, large-thickness, closed- section tubular carbon fiber beam according to claim 1, characterized by: The process of step S3 is specifically as follows: First, the laid upper beam preform and the first lower beam preform are demolded and transferred to the second lower beam mold, the R-angle positions on both sides are supplemented with prepreg, the mold upper cover plate is covered, and the mold is fixed by closing.

5. The method of manufacturing a non-equal- diameter, large-thickness, closed- section tubular carbon fiber beam according to claim 1, characterized by: The detection of whether the vacuum bag meets the standard is specifically as follows: Transport the mold to the autoclave platform, connect to the vacuum system, apply a vacuum pressure of -0.085 MPa or less, and apply an air pressure of 0.6 MPa, hold for at least 5 min with no leaks, turn off the vacuum system, and the vacuum gauge reading should not decrease by more than 0.02 MPa in 5 min; Otherwise, check and repair the vacuum bag, and if it cannot meet the standard, repackage the vacuum bag.

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