A preparation method of a combined containment cartridge preform RTM injection molding

Abstract

The application discloses a preparation method of a combined containment cartridge preform RTM injection molding in the technical field of composite material forming, and comprises the following steps: S1, preparing a metal cartridge as a structural framework, wherein the shape and mounting structure of the metal cartridge are adapted to subsequent composite material assembly; S2, preparing a fiber preform which is adapted to the shape of the metal cartridge by using a three-dimensional weaving process; and S3, assembling the fiber preform which has been subjected to preforming treatment together with the metal cartridge in a combined RTM mold, and performing one-time injection molding and curing by using a vacuum-assisted resin transfer molding process to form a metal-composite integrated containment ring. By using precision machining of the titanium alloy cartridge through a numerical control vertical lathe and a vertical gantry milling machine, and by using fluorescent flaw detection full-range defect investigation and surface cleanliness control, the application effectively reduces the overall structural failure risk caused by metal matrix defects or poor adhesion, and builds a foundation for metal-composite integrated forming.

Description

Technical Field

[0001] This invention relates to the field of composite material molding technology, and more specifically, to a method for preparing a preform of a combined housing by RTM injection molding. Background Technology

[0002] As a core supporting component, the casing of an aero-engine is directly related to the flight stability and reliability of the aircraft. The key lies in whether it can effectively block high-speed impact fragments generated by the failure of internal engine parts, and avoid secondary damage to the aircraft skin, fuel tank, control circuits, etc. after the fragments penetrate. Therefore, there are strict requirements for the structural strength, impact resistance and lightweight level of the casing.

[0003] Currently, metal casings are widely used in the field of aero-engines. These casings can meet the basic support and protection requirements due to their mechanical properties. With the development of composite material technology, some casings have begun to be made of composite materials with laminated plate structures in an attempt to improve the limitations of traditional metal casings.

[0004] However, existing technologies still have certain problems: On the one hand, traditional metal casings are heavy, making it difficult to adapt to the trend of lightweight development in aviation equipment, and their performance is limited in high-temperature environments. When the engine blades rub against the casing, safety hazards are easily generated. At the same time, their thermal conductivity is poor, and heat is not easily dissipated during processing, which increases the processing difficulty and makes the manufacturing process of large metal casings more complex. On the other hand, composite material casings with laminated plate structures have the inherent defect of low interlaminar shear strength. They are prone to delamination and damage when subjected to high-speed impacts, making it difficult to meet the high containment performance requirements of the casing and failing to fully guarantee the flight safety of aircraft. Therefore, we urgently need a method for preparing prefabricated modular containment casings by RTM injection molding to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a new technical solution for the preparation of a combined enclosure casing preform by RTM injection molding. Through precise machining of the titanium alloy casing, three-dimensional weaving of the fiber preform, and integrated RTM molding and secondary curing, a tight bond between the metal and composite materials is achieved, thereby improving the structural strength and impact resistance of the enclosure casing.

[0006] The objective of this invention is achieved as follows: a method for preparing a combined enclosure casing preform by RTM injection molding, comprising the following steps:

[0007] S1: Prepare a metal casing as a structural frame, the shape and mounting structure of the metal casing being adapted to subsequent composite material assembly;

[0008] S2: A fiber preform adapted to the shape of the metal casing is prepared using a three-dimensional weaving process;

[0009] S3: After the fiber preform is pre-shaped, it is assembled together with the metal casing into a combined RTM mold, and then injection molded and cured in one step through a vacuum-assisted resin transfer molding process to form an integrated metal-composite material containment ring.

[0010] S4: The enclosing ring is machined to the final designed shape;

[0011] S5: A reinforcing layer is applied to the outer surface of the processed containment ring and then cured a second time to obtain the combined containment casing.

[0012] Optionally, in step S1, the metal casing is a titanium alloy casing, and its processing includes machining the inner and outer surfaces using a CNC vertical lathe, machining the mounting edges and end holes using a vertical gantry milling machine, and performing fluorescent flaw detection after processing.

[0013] Optionally, in step S2, the fiber preform is woven from high-strength, high-modulus polyimide fibers. The weaving process includes warping, heddle threading, opening, weft insertion, weft beat-up, and reed lifting. The weaving density of the preform includes warp density and weft density, with a warp density of 8-9 threads / cm and a weft density of 2-4 threads / cm.

[0014] Optionally, in step S3, the combined RTM mold includes an inner ring module and an outer ring module for positioning the metal casing, and the sealing structure of the mold includes at least two silicone sealing strips disposed in the sealing groove, with the joints of each sealing strip arranged in a staggered manner.

[0015] Optionally, in step S3, the one-time injection molding and curing includes: evacuating the closed mold cavity, degassing the injection resin under vacuum, injecting resin after the mold temperature reaches 100-120℃ and the cavity vacuum degree is ≤-0.095MPa, maintaining pressure at 0.3-0.6MPa for 10-60 minutes after injection, and then performing segmented temperature rise curing.

[0016] Optionally, the final curing stage temperature of the segmented heating and curing is 240°C to 260°C, and the holding time is not less than 4 hours.

[0017] Optionally, in step S5, the reinforcing layer is a glass fiber prepreg layer, and the secondary curing is a curing process carried out under vacuum bag pressure.

[0018] Optionally, the secondary curing process includes a segmented heating stage, and the final curing stage temperature is not lower than 240°C.

[0019] Optionally, after the secondary curing is completed, the temperature is reduced to below 60°C at a rate not exceeding 1°C / min, and then the pressure is released and the can is opened.

[0020] Optionally, step S5 specifically includes: cleaning the surface of the machined containment ring, applying a layer of adhesive film, and then applying glass cloth prepreg; subsequently, laying out a peelable cloth, a release film, a breathable felt, and a vacuum bag film in sequence; sealing the bag with sealing strips and then curing it.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. According to one embodiment of this disclosure, the method for preparing the prefabricated modular housing by RTM injection molding uses CNC vertical lathe and vertical gantry milling machine to precisely process the titanium alloy housing, combined with full-range defect screening by fluorescent flaw detection and surface cleanliness control. This effectively ensures the dimensional accuracy, structural integrity and assembly compatibility of the metal skeleton, effectively reduces the risk of overall structural failure due to defects in the metal matrix or poor bonding, and lays a solid foundation for the integrated molding of metal-composite materials.

[0023] 2. According to one embodiment of this disclosure, the method for preparing the prefabricated composite housing by RTM injection molding employs a three-dimensional weaving process with the axial direction as warp and the circumferential direction as weft, combined with multiple refined operations such as warp grouping and fixing, and heddle and reed density control, to prepare a fiber prefabricated body that is precisely adapted to the shape of the metal housing and has a tight and uniform structure. This significantly improves the mechanical strength and integrity of the composite material housing ring, provides reliable core reinforcement support for the housing, and effectively strengthens its impact resistance.

[0024] 3. According to one embodiment of this disclosure, the method for preparing the combined housing preform by RTM injection molding utilizes a multi-stage staggered silicone sealing strip design in the combined RTM mold, strict control of the mold closing gap, and vacuum-assisted resin transfer molding process. Combined with the resin vacuum degassing and segmented temperature curing process, this method achieves uniform and sufficient impregnation of the fiber preform by the resin, promotes the tight cross-linking of the metal and composite materials, effectively reduces molding defects such as internal pores and missing glue in the housing ring, and improves the density and bonding strength of the integrated structure.

[0025] 4. According to one embodiment of this disclosure, the method for preparing the prefabricated modular enclosure housing by RTM injection molding involves dual quality control through appearance inspection after machining and ultrasonic non-destructive testing. Combined with the laying of the outer glass cloth reinforcement layer and the secondary curing process of vacuum bag pressing and autoclave, it not only ensures the dimensional accuracy and defect-free state of the enclosure housing, but also further enhances the integrity and protective performance of the overall structure. Finally, a modular enclosure housing with the stable support of the metal frame and the excellent impact resistance of the composite material is formed, which meets the high performance and high reliability requirements of high-end equipment for the enclosure housing. Attached Figure Description

[0026] 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.

[0027] Figure 1 This is a flowchart of the present invention.

[0028] Figure 2 This is a schematic diagram of the combined enclosure casing of the present invention.

[0029] Figure 3 This is a schematic diagram of the RTM mold of the present invention.

[0030] Figure 4 This is a schematic diagram of the mold assembly for injection molding according to the present invention.

[0031] Figure 5 This is a schematic cross-sectional view of the enclosing ring of the present invention.

[0032] Figure 6 This is a schematic diagram of the glass cloth laying process according to the present invention.

[0033] The following are marked in the diagram: 1. Composite material housing ring; 2. Titanium alloy housing; 3. Mounting flange hole; 4. Outer ring module; 5. Silicone sealing strip; 6. Outer ring insert; 7. Inner ring insert; 8. Lifting lug; 9. Inner ring module; 10. Upper template; 11. Lower template; 12. Glue injection hole; 13. Outer layer of glass cloth. Detailed Implementation

[0034] 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.

[0035] like Figure 1-6 As shown, a method for preparing a modular enclosure preform by RTM injection molding includes the following steps:

[0036] S1: Prepare a metal casing as a structural skeleton. The shape and installation structure of the metal casing are adapted to the subsequent assembly of composite materials.

[0037] In step S1, the metal casing is a titanium alloy casing 2. Its processing includes machining the inner and outer surfaces using a CNC vertical lathe, and machining the mounting edge and mounting structure using a vertical gantry milling machine. The mounting structure is preferably the mounting edge flange hole 3. After machining, it needs to be inspected by fluorescent flaw detection.

[0038] Here, CNC vertical lathe machining must ensure the dimensional accuracy and surface finish of the inner and outer surfaces of the titanium alloy housing 2. When machining the front and rear mounting edges and mounting edge flange holes 3 with the vertical gantry milling machine, it must be ensured that the position of the mounting structure meets the assembly requirements. Before machining, it is necessary to ensure the basic accuracy of the titanium alloy housing 2 as the structural skeleton. The basic accuracy can provide a guarantee for the subsequent accurate assembly with the fiber preform.

[0039] Furthermore, fluorescent flaw detection needs to cover the inner and outer surfaces of the titanium alloy casing 2, the mounting edge, and the area around the mounting edge flange hole 3, focusing on identifying internal and surface defects such as cracks and inclusions. Using fluorescent flaw detection can prevent the defective titanium alloy casing 2 from entering subsequent processes, reducing the risk of overall structural failure of the combined enclosure casing.

[0040] Furthermore, the processed titanium alloy casing 2 must be kept clean to avoid the residue of oil, iron filings and other impurities, and there must be no debris blocking the mounting flange hole 3; keeping the surface clean of the titanium alloy casing 2 can prevent impurities from affecting the subsequent bonding with the fiber preform and the resin impregnation effect, ensuring the quality of the integrated molding of metal-composite materials, and at the same time avoiding the blockage of the mounting flange hole 3 from affecting subsequent assembly.

[0041] S2: A fiber preform adapted to the shape of the metal casing is prepared using a three-dimensional weaving process.

[0042] In step S2, the fiber preform is woven from 200tex high-strength, high-modulus polyimide fiber filaments. The weaving process includes warping, heddle threading, shedding, weft insertion, beating, and reed lifting. The weaving density of the preform includes warp density and weft density, with a warp density of 8-9 threads / cm and a weft density of 2-4 threads / cm. The fiber volume content of the fiber preform is 48±2%, preferably 8.5 warp threads / cm and 3 weft threads / cm. During weaving, the axial direction of the machine casing is taken as the warp direction and the circumferential direction is taken as the weft direction.

[0043] Here, during the warping process, the warp yarns are pulled up, and one end of each warp yarn is fixed to the hook of the weaving equipment in sequence, with a specified number of yarns per group. The warp yarns are then wound onto the warp beam at a set tension, and each warp yarn end is threaded through an elastic rope and fixed, so that the weft yarn can be tightly woven onto the warp yarn, preventing the yarn from becoming loose during the weaving process. This ensures the tightness of the preform weaving and lays the foundation for improving the structural strength of the composite material containment ring 1 that is subsequently formed.

[0044] Furthermore, during heddle threading, each warp yarn is passed through the heddle eye in the heddle frame one by one by threading a needle. During the operation, it is necessary to avoid warp yarn breakage or twisting. Reed threading is done by hand, passing the warp yarns through the reed teeth one by one in a regular pattern to precisely control the warp yarn density. The above methods can ensure that the warp yarn arrangement meets the design requirements, ensure the uniformity of the weaving density of the prefabricated body, avoid local density deviations, and make the prefabricated body perfectly compatible with the titanium alloy housing 2.

[0045] Furthermore, the opening is formed by the up-and-down movement of the heald frame to create the warp shed. The yarns of each heald frame are grouped together, and the warp tension is adjusted with the help of elastic ropes and manual assistance for opening. Weft insertion is done manually, with the weft yarn wound around the heald shuttle and inserted from the bottom warp layer. After weft insertion, the reed is lifted by moving it up and down, moving it every other reed to maintain a positional difference of two reed teeth between adjacent reeds before fixing it. The above-mentioned opening method can achieve precise interlacing of warp and weft yarns, ensuring the molding quality of the fiber preform and providing structural support for the high strength and high integrity of the subsequent composite material containment ring 1.

[0046] S3: After the fiber preform is pre-shaped, it is assembled with the metal casing into a combined RTM mold, and then injected and cured in one step through a vacuum-assisted resin transfer molding process to form an integrated metal-composite material containment ring.

[0047] Here, the pre-forming process uses a pre-formed adhesive to treat the fiber preform, ensuring that the preform maintains a shape compatible with the titanium alloy casing 2. The pre-forming is to fix the fibers, making it easier to install and close the mold. The modular RTM mold is preferably made of 45# steel. The modular RTM mold includes an inner ring module 9, an outer ring module 4, an outer ring insert 6, an inner ring insert 7, an upper template 10, a lower template 11, and lifting lugs 8. During assembly, the fitting accuracy of each module and insert must be confirmed first. This pre-forming process ensures the stability of the fiber preform's shape during assembly and adhesive injection, while also guaranteeing the fitting accuracy of each component of the modular RTM mold, providing structural support for the integrated molding of the composite material containment ring 1.

[0048] Furthermore, before using the combined RTM mold, the surfaces of the tooling, including the inner ring module 9, outer ring module 4, outer ring insert 6, inner ring insert 7, upper template 10, and lower template 11, should be cleaned with a lint-free cloth dampened with an appropriate amount of acetone until the cloth shows no obvious discoloration. After air-drying at room temperature for at least 15 minutes, the tooling surfaces should be wiped with a lint-free cloth dampened with 770NC release agent at least three times, with an interval of at least 15 minutes between each wipe. This cleaning operation can effectively remove impurities from the surfaces of various parts of the mold, preventing impurities from affecting the resin molding effect. The proper use of the release agent can ensure the smooth demolding of the composite material containment ring 1 and prevent surface damage.

[0049] Furthermore, before using the mold, the mold closing gaps between the upper mold plate 10 and the lower mold plate 11, the outer ring module 4 and the outer ring insert 6, and the inner ring module 9 and the inner ring insert 7 are checked using modeling clay. The gaps are preferably no more than 0.1mm. After the check, the problem of glue leakage during injection can be avoided due to excessive gaps between the mold components, ensuring the sealing of RTM injection molding and improving the molding quality of the composite material containment ring 1.

[0050] In step S3, the combined RTM mold includes an inner ring module 9 and an outer ring module 4 for positioning the metal casing. The sealing structure of the mold includes at least two silicone sealing strips 5 disposed in the sealing groove, and the joints of each silicone sealing strip 5 are staggered.

[0051] Here, the interface of the silicone sealing strip 5 is treated with a beveled edge to ensure good fit of the joints of each sealing strip. The two silicone sealing strips 5 are respectively installed in the sealing grooves of the outer ring module 4 and the inner ring module 9. The beveled edge treatment can effectively improve the sealing effect of the silicone sealing strip 5, specifically strengthen the sealing performance of the inner and outer rings of the mold, and reduce the risk of vacuum leakage.

[0052] Furthermore, the interfaces of the two silicone sealing strips 5 must not be located on the same side of the mold, and during installation, it must be ensured that the silicone sealing strips 5 are fully fitted with the sealing groove without twisting or wrinkling; the separate design of the interfaces can avoid the concentration of weak points in the seal, further enhance the sealing performance of the mold cavity, and provide a stable environment for the vacuum injection of the composite material containment ring 1.

[0053] Furthermore, when closing the mold, it is necessary to check the positioning and fit of the outer ring insert 6 and the inner ring insert 7 to ensure that the gap between the upper mold plate 10 and the lower mold plate 11 is uniform after mold closing. At the same time, it is confirmed that the lifting lug 8 is firmly installed. The gap between the preform and the mold is preferably less than 0.05mm. After the preform is properly trimmed, the pressure air pipe is connected to the glue injection hole 12, the glue injection valve is opened and the glue outlet valve is closed. The pressure in the mold cavity is adjusted to 0.5MPa. Soap water is sprayed onto the mold closing surface with a spray bottle to check whether the mold is leaking. The above operations can ensure the mold closing accuracy and sealing, avoid the resin flow obstruction caused by the positioning deviation of the insert and uneven gap, ensure the safety of mold transfer due to the firmness of the lifting lug 8, and accurately find the leak point by using soap water to ensure that there is no leakage during the glue injection process.

[0054] In step S3, the one-time injection molding and curing includes: evacuating the closed mold cavity, degassing the injection resin under vacuum, injecting resin after the mold temperature reaches 100-120℃ and the cavity vacuum degree is ≤-0.095MPa, holding the pressure at 0.3-0.6MPa for 10-60 minutes after injection, preferably at 0.5MPa for 15 minutes, followed by segmented temperature rise curing; the injection resin is RTM bismaleimide resin.

[0055] Here, during vacuuming, first install the glue injection pipeline and the glue outlet vacuum pipeline connected to the glue injection hole 12, close the glue outlet valve, open the flow control valve, the glue outlet valve and the glue outlet pressure control valve, start the vacuum pump to vacuum, and after the oven heats up to the specified temperature, transfer the mold to the oven through the lifting lug 8 to continue vacuuming and preheating. The vacuum degree inside the mold is preferably evacuated to <-0.095MPa. The above operations can ensure that the mold cavity and surrounding environment meet the glue injection requirements, the pipeline connection of the glue injection hole 12 is standardized and the lifting lug 8 is safely transferred, creating stable conditions for the resin to uniformly impregnate the preform.

[0056] Furthermore, during vacuum degassing of the resin, the prepared resin needs to be poured into the dispensing bucket, placed in the dispensing tank, and closed. The vacuum valve of the dispensing tank is then opened for degassing. The degassing time is preferably 20 minutes to prevent large molecules in the resin from being released. During injection, the resin is slowly injected through the dispensing hole 12. After opening the flow rate control valve, the resin flow rate is controlled within the process design range. The injection pressure is adjusted appropriately according to the resin flow rate and the air bubbles in the outlet hose, with a preferred injection pressure of 0.4 MPa, until the dispensing port stably dispenses resin. Using degassing treatment to remove resin air bubbles can avoid pore defects inside the containment ring. Precise control of flow rate and pressure effectively ensures that the resin can uniformly and fully impregnate the fiber preform, ensuring that there is no localized resin deficiency.

[0057] Furthermore, once the amount of adhesive dispensed from the dispensing tank reaches the limit, the vacuuming process automatically stops and the dispensing valve is closed. The pressure is maintained through the dispensing hole 12 to ensure the pressure holding effect. This promotes the tight bonding between the resin and the fiber and the titanium alloy casing 2, further enhancing the compactness and bonding strength of the composite material containment ring 1.

[0058] The final curing temperature of the segmented heating curing is 240℃ to 260℃, and the holding time is not less than 4 hours. The preferred final curing temperature is 250℃±5℃ and the holding time is 6 hours.

[0059] Here, the heating rate of the segmented heating curing is no higher than 1.5℃ / min. First, the mold temperature is raised to 125℃±5℃ and held for 0.5h. During this process, the temperature consistency of the inner ring module 9 and the outer ring module 4 is monitored in real time by the temperature sensor of the mold. The segmented heating curing operation allows the resin to gradually adapt to the temperature change, avoids uneven resin reaction due to excessive heating, and ensures that the temperature of each area of ​​the mold is consistent, thus ensuring that the curing of each part of the composite material containing ring 1 is synchronized.

[0060] Furthermore, the temperature is raised to 185℃±5℃ at the same rate and held for 1 hour, then raised to 230℃±5℃ and held for 2 hours. During each stage of holding, the mold cavity must be kept sealed. This staged heating can promote the resin crosslinking reaction, ensure that the reaction is sufficient and thorough, and avoid insufficient stability of the composite material's encapsulated ring 1 structure due to incomplete curing.

[0061] Furthermore, after heating to the optimal temperature, the temperature is held for the optimal time to ensure complete resin curing. After curing, the temperature is allowed to cool naturally to a suitable temperature before subsequent operations are performed. The final heating stage can fully guarantee the bonding strength between the titanium alloy casing 2 and the composite material, enabling the composite material containing ring 1 to form a stable integrated structure, significantly improving the overall mechanical properties and impact resistance.

[0062] S4: Machin the containment ring to the final designed shape.

[0063] Here, machining is performed using a machining center to precisely process the composite material containment ring 1 according to its design shape. This ensures that the shape of the containment ring meets the assembly requirements and provides a good bonding foundation for the subsequent application of the outer reinforcement layer.

[0064] Furthermore, the location of the mounting flange hole 3 must be avoided during processing to ensure that the mounting structure is not damaged. At the same time, the machining speed and feed rate should be reasonably controlled to avoid the cracking of the containment ring caused by machining stress. This further protects the assembly accuracy of the mounting flange hole 3, reduces structural damage during processing, and ensures the overall structural integrity of the containment ring.

[0065] Furthermore, after machining, the containment ring needs to undergo a visual inspection to check for defects such as inclusions, delamination, wrinkles, white spots, and glue buildup on the surface. At the same time, ultrasonic equipment is used to perform non-destructive testing on the internal quality of the containment ring. After machining, a comprehensive inspection of the surface and internal defects of the containment ring is required to prevent unqualified products from entering subsequent processes and to effectively ensure the final quality of the modular containment housing.

[0066] S5: A reinforcing layer is applied to the outer surface of the processed containment ring and then cured a second time to obtain a combined containment casing.

[0067] In step S5, the reinforcing layer is a glass fiber prepreg layer, and the secondary curing is a thermostatic curing process carried out in a vacuum bag pressure environment. The secondary curing process includes a segmented heating stage, and the final curing stage temperature is not lower than 240℃, preferably 250℃±5℃.

[0068] Before applying the reinforcing layer, the surface of the machined composite material housing ring 1 should be cleaned with anhydrous ethanol to remove dust, oil, and other impurities. At the same time, check whether the joint between the composite material housing ring 1 and the titanium alloy casing 2 is flat. After cleaning, first apply a layer of adhesive film to the surface of the housing ring 1, and then apply the fiberglass prepreg to strengthen the bond between the two. The cleaning before application can ensure the adhesion between the outer glass cloth 13 and the surface of the composite material housing ring 1, and avoid impurities or uneven joints affecting the bonding effect, so as to give full play to the protective function of the reinforcing layer.

[0069] Furthermore, the vacuum bag pressure environment is formed by laying auxiliary materials and sealing the bag. The auxiliary materials include peelable cloth, release film, breathable felt and vacuum bag film. When laying, it is necessary to completely cover the entire surface of the reinforcing layer. The reinforcing layer is preferably the outer glass cloth 13. The above operation can provide a stable vacuum environment for secondary curing, ensuring that the outer glass cloth 13 is tightly bonded to the composite material containment ring 1, and improving the integrity of the overall structure.

[0070] Furthermore, the segmented heating stage of the secondary curing follows the same heating rate control requirements as the primary curing. However, it should be noted that the heating rate should not exceed 1.5℃ / min, thereby ensuring a stable curing process and avoiding adverse effects of temperature fluctuations on the bonding between the composite material housing ring 1 and the outer glass cloth 13. The segmented heating of the secondary curing avoids stress at the bonding between the reinforcing layer and the composite material housing ring 1 caused by fluctuations in the heating rate, thus improving the overall structural stability and durability of the combined housing.

[0071] Step S5 specifically includes: after cleaning the surface of the machined containment ring, laying a reinforcing layer, preferably an outer layer of glass cloth 13; then laying a peelable cloth, a release film, a breathable felt, and a vacuum bag film in sequence; sealing the bag with sealing strips and then curing it.

[0072] Here, when laying the outer glass cloth 13, it is necessary to ensure that the sheet is completely attached to the outer surface of the composite material containment ring 1, without any defects such as wrinkles or bubbles. The coverage area of ​​the outer glass cloth 13 should completely wrap the outer area of ​​the composite material containment ring 1. The above operations can ensure the uniformity of the reinforcement layer coverage, give full play to the protective and reinforcing role of the outer glass cloth 13 on the composite material containment ring 1, and improve the impact resistance of the combined containment casing.

[0073] Furthermore, when laying the peelable cloth, the isolation film, the breathable felt and the vacuum bag film in sequence, it is necessary to ensure that each layer of material is laid flat, without overlap or damage, and completely covers the outer glass cloth 13 to avoid local exposure; by ensuring the vacuum bag compression effect, it is possible to avoid poor secondary curing quality due to improper laying of auxiliary materials, and to ensure the bonding strength between the outer glass cloth 13 and the composite material containment ring 1.

[0074] Furthermore, during the sealing process, sealing strips are used to tightly seal the edges of the vacuum bag film to ensure that the sealing performance after bag making meets the requirements of secondary curing. After curing, the temperature is lowered to below 60°C at a rate not exceeding 1°C / min, then the pressure is released and the can is opened. After cooling to room temperature, the vacuum bag film is removed. The above operations can prevent vacuum leakage during the secondary curing process, and the standardized cooling can avoid cracking caused by thermal stress. Removing the film after cooling to room temperature can protect the surface quality of the reinforcing layer and comprehensively improve the quality of the combined enclosure.

[0075] In this invention, a titanium alloy casing 2 is used as the structural skeleton. The inner and outer surfaces and mounting flange holes 3 are precisely machined by CNC vertical lathe and vertical gantry milling machine. Fluorescent flaw detection is used to ensure its basic accuracy, structural integrity and surface cleanliness. The mounting flange holes 3 can ensure the assembly position of the titanium alloy casing 2 with other components, laying a solid foundation for subsequent assembly of the whole machine and the adaptation and connection with composite materials. Subsequently, a three-dimensional weaving process is used to prepare a 200tex high-strength and high-modulus polyimide fiber preform with uniform density and precise fit to the shape of the titanium alloy casing 2, with the casing axis as the warp and the circumferential direction as the weft. Through strict control of multiple processes such as warping, heddle threading, opening, weft insertion, weft beater and reed lifting, the preform structure is ensured to be compact, providing core reinforcement support for the composite material containment ring 1.

[0076] After pre-forming, the preform is assembled with the titanium alloy casing 2 into a combined RTM mold consisting of an inner ring module 9, an outer ring module 4, an outer ring insert 6, an inner ring insert 7, an upper template 10, a lower template 11, and lifting lugs 8. The mold is controlled by at least two staggered silicone sealing strips 5 and the mold closing gap to ensure the stability of the vacuum environment in the cavity. Then, RTM bismaleimide resin, which has been vacuum degassed, is injected into the preform through the injection hole 12 under set temperature and pressure conditions. Combined with a segmented temperature-curing process, the resin is fully cross-linked to achieve a tight bond and integrated molding of the metal and composite materials, forming a composite material containment ring 1. The molded composite material containment ring 1 is precisely dimensionally controlled by machining and defects are checked by visual inspection and ultrasonic non-destructive testing. Finally, an outer layer of glass cloth 13 is laid on its outer surface as a reinforcing layer. The secondary curing process using a vacuum bag press further improves the overall structural integrity and impact resistance, ultimately forming a combined containment casing that combines the supporting strength of a metal skeleton with the excellent protective performance of a composite material.

[0077] 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 preparing a prefabricated modular housing by RTM injection molding, characterized in that: Includes the following steps: S1: Prepare a metal casing as a structural frame, the shape and mounting structure of the metal casing being adapted to subsequent composite material assembly; S2: A fiber preform adapted to the shape of the metal casing is prepared using a three-dimensional weaving process; S3: After the fiber preform is pre-shaped, it is assembled together with the metal casing into a combined RTM mold, and then injection molded and cured in one step through a vacuum-assisted resin transfer molding process to form an integrated metal-composite material containment ring. S4: The enclosing ring is machined to the final designed shape; S5: A reinforcing layer is applied to the outer surface of the processed containment ring and then cured a second time to obtain the combined containment casing.

2. The preparation method of a combined enclosure casing preform by RTM injection molding according to claim 1, characterized in that: In step S1, the metal casing is a titanium alloy casing, and its processing includes machining the inner and outer surfaces using a CNC vertical lathe, machining the mounting edges and end holes using a vertical gantry milling machine, and performing fluorescent flaw detection after processing.

3. The method for preparing a prefabricated modular enclosure housing by RTM injection molding according to claim 1, characterized in that: In step S2, the fiber preform is woven from high-strength, high-modulus polyimide fibers. The weaving process includes warping, heddle threading, opening, weft insertion, weft beat-up, and reed lifting. The weaving density of the preform includes warp density and weft density, with a warp density of 8-9 threads / cm and a weft density of 2-4 threads / cm.

4. The preparation method of a combined enclosure casing preform by RTM injection molding according to claim 1, characterized in that: In step S3, the combined RTM mold includes an inner ring module and an outer ring module for positioning the metal casing. The sealing structure of the mold includes at least two silicone sealing strips disposed in the sealing groove, and the joints of the sealing strips are staggered.

5. The method for preparing a prefabricated modular enclosure housing by RTM injection molding according to claim 1, characterized in that: In step S3, the one-time injection molding and curing includes: evacuating the closed mold cavity, degassing the injection resin under vacuum, injecting resin after the mold temperature reaches 100-120℃ and the cavity vacuum degree is ≤-0.095MPa, maintaining pressure at 0.3-0.6MPa for 10-60 minutes after injection, and then performing segmented temperature rise curing.

6. The method for preparing a combined enclosure casing preform by RTM injection molding according to claim 5, characterized in that: The final curing stage temperature of the segmented heating and curing process is 240°C to 260°C, and the holding time is no less than 4 hours.

7. The method for preparing a combined enclosure casing preform by RTM injection molding according to claim 1, characterized in that: In step S5, the reinforcing layer is a glass fiber prepreg layer, and the secondary curing is a curing process carried out under vacuum bag pressure.

8. The method for preparing a combined enclosure casing preform by RTM injection molding according to claim 1, characterized in that: The secondary curing process includes a segmented heating stage, and the final curing stage temperature is not lower than 240°C.

9. The method for preparing a combined enclosure casing preform by RTM injection molding according to claim 8, characterized in that: After the secondary curing is completed, the temperature is reduced to below 60°C at a rate not exceeding 1°C / min, and then the pressure is released and the can is opened.

10. The method for preparing a prefabricated modular enclosure housing by RTM injection molding according to claim 1, characterized in that: Step S5 specifically includes: after cleaning the surface of the machined containment ring, laying a layer of adhesive film and then laying a layer of glass cloth prepreg; then laying a peelable cloth, a release film, a breathable felt and a vacuum bag film in sequence; sealing the bag with sealing strips and then curing it.

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