A carbon fiber composite hat stringer preform system and method

Abstract

The application discloses a kind of carbon fiber composite material hat-shaped stringer preforming system and method, belong to composite material forming field.Preforming system includes hot mould pressing special mould, mould temperature machine system for temperature regulation and control, distributed pressure sensing network for monitoring pressure distribution in preparation process and displacement control system for controlling mould pressing displacement.Preforming method is by temperature regulation and control and mould pressing displacement, and in preset displacement node, automatic interruption is carried out to the process of pressing down, and the preformed body is taken out from special mould after heat preservation ends, to realize hat-shaped stringer preformed body preparation.The preforming system of the application has high displacement control precision, not only can form thermosetting carbon fiber reinforced resin matrix prepreg, but also is suitable for preforming process of high modulus thermoplastic carbon fiber reinforced resin matrix prepreg and dry fiber cloth.

Description

Technical Field

[0001] This invention belongs to the field of composite material molding, specifically relating to a carbon fiber composite material hat-shaped stringer preforming system and method. Background Technology

[0002] Carbon fiber composite cap stringers are key load-bearing components in modern aircraft fuselage structures, and their molding quality directly determines the overall load-bearing capacity and safety reliability of the fuselage structure. In aircraft manufacturing, cap stringers first need to be preformed and then co-cured with fuselage panels to achieve high-quality bonding. Currently, the main manufacturing processes for cap stringer preforms include manual lay-up molding and hot molding. Comparatively, hot molding has become the mainstream choice for cap stringer preform manufacturing in the aerospace industry due to its superior molding efficiency, good process repeatability, and significant cost advantages.

[0003] In the prior art, patent CN111746003B discloses a long stringer hot molding preforming equipment and method, which indirectly controls the molding quality by setting a pressure monitoring system on the mold surface. However, this method is difficult to guarantee the uniformity of pressure distribution in different areas inside the component, and has the limitation of insufficient control precision. Patent CN120245471A proposes a composite material long stringer molding mold and method for thermosetting carbon fiber reinforced resin-based prepregs, but it lacks applicability to the preforming process of materials such as thermoplastic carbon fiber reinforced resin-based prepregs and dry fiber cloth with high modulus.

[0004] Therefore, there is an urgent need to provide a new carbon fiber composite cap-shaped stringer preforming system and method to solve the above-mentioned technical bottlenecks. Summary of the Invention

[0005] The purpose of this invention is to overcome the deficiencies in the prior art and provide a carbon fiber composite cap-shaped stringer preforming system and method. This invention integrates a dedicated hot-molding mold, a mold temperature control system, a distributed pressure sensing network, and a displacement control system. By presetting process parameters and terminating the pressing process at key displacement nodes, it achieves high-precision fabrication of carbon fiber composite cap-shaped stringer preforms.

[0006] The specific technical solution adopted in this invention is as follows:

[0007] In a first aspect, the present invention provides a carbon fiber composite material hat-shaped stringer preforming system, including a hot molding special mold, a mold temperature control system, a distributed pressure sensing network and a displacement control system.

[0008] The hot molding die includes a lower support die assembly and an upper support die assembly. A lower pressure plate is fixed to the lower side of the lower support die assembly, and a lower die block assembly is fixed to the upper side. An upper die block assembly is fixed to the lower side of the upper support die assembly, and an upper pressure plate is fixed to the upper side. A prepreg layer is placed between the upper die block assembly and the lower die block assembly. Several vertical sliding shafts connect the upper and lower support die assemblies. The upper and lower pressure plates are respectively connected to a displacement control system, which controls the downward displacement of the upper pressure plate relative to the lower pressure plate, thus changing the vertical distance between the upper and lower support die assemblies. The upper and lower support die assemblies are connected to a mold temperature control system for regulating the temperature of the prepreg layer via a water pipe assembly. Several thin-film pressure sensors are provided on one side of the upper and lower die block assemblies that contact the prepreg layer. All the thin-film pressure sensors together form a distributed pressure sensing network for monitoring the pressure distribution on the prepreg layer during the manufacturing process.

[0009] Preferably, the lower mold block assembly includes a lower right mold block, a lower middle mold block, and a lower left mold block, which together form a central concave structure. The lower right and lower left mold blocks are fixed to the upper surface of the lower support mold assembly by bolts, and the bottom of the lower middle mold block is connected to the upper surface of the lower support mold assembly by a spring that provides vertical elasticity. The upper mold block assembly includes an upper right mold block, an upper middle mold block, and an upper left mold block, which together form a central convex structure. The upper middle mold block is fixed to the lower surface of the upper support mold assembly by bolts, and the tops of the upper right and upper left mold blocks are respectively connected to the lower surface of the upper support mold assembly by springs that provide vertical elasticity. The central concave structure and the central convex structure are matched to form a mold space for the prepreg layer to form a hat-shaped stringer structure.

[0010] Furthermore, the lower right mold block and the lower left mold block are respectively symmetrically provided with a number of positioning pins for controlling the size of the prepreg layer, and the diameter tolerance of each positioning pin is ±0.01mm and the positioning accuracy is ±0.05mm.

[0011] Furthermore, the lower right mold block, the lower left mold block, and the upper middle mold block are respectively horizontally embedded with a first thermocouple, a second thermocouple, and a third thermocouple in their middle portions; the temperature monitoring range of each thermocouple is 0~400℃, the temperature monitoring accuracy is ±1℃, and the embedding depth is ≥15mm.

[0012] Preferably, the water pipe assembly includes a first water pipe, a second water pipe, a third water pipe, and a fourth water pipe;

[0013] One end of the first water pipe is connected to the heat medium outlet of the mold temperature controller system, and the other end is connected to the upper support mold assembly; one end of the second water pipe is connected to the upper support mold assembly, and the other end is connected to the heat medium inlet of the mold temperature controller system; the mold temperature controller system forms a first heat exchange medium circuit with the upper support mold assembly through the first water pipe and the second water pipe.

[0014] One end of the third water pipe is connected to the heat medium outlet of the mold temperature controller system, and the other end is connected to the lower support mold assembly; one end of the fourth water pipe is connected to the lower support mold assembly, and the other end is connected to the heat medium inlet of the mold temperature controller system; the mold temperature controller system forms a second heat exchange medium circuit with the lower support mold assembly through the third and fourth water pipes.

[0015] The mold temperature control system uses the first heat exchange medium circuit and the second heat exchange medium circuit to uniformly control the temperature of the upper and lower surfaces of the prepreg layer.

[0016] Preferably, the prepreg layer is a thermosetting or thermoplastic carbon fiber reinforced resin-based prepreg or dry fiber cloth.

[0017] Preferably, the displacement control system is a universal testing machine, used to automatically interrupt the molding process at preset process nodes, with an interruption time resolution of ±0.1s, a displacement control accuracy of 0.001mm, a loading rate of 0.1-20mm / min, and a rated force of 250kN.

[0018] Preferably, the mold temperature control system includes a filter, a heating pump, a cooling solenoid valve, a temperature sensor, an electrical control box, and a heater, all fixed to a frame. The inlet of the heating pump is connected to both a cold medium inlet and a hot medium inlet via pipes, and its outlet is connected to the heater. A filter is installed on the pipe leading out of the cold medium inlet. The heater is connected to the hot medium outlet via a pipe equipped with a temperature sensor, and the hot medium inlet is also connected to the cold medium outlet via a pipe equipped with a cooling solenoid valve.

[0019] The internal heat transfer medium of the mold temperature controller system is water or oil; the electrical control box adopts a PID control algorithm with a temperature control accuracy of ±1℃, so that the temperature difference on the surface of the prepreg layer is ≤±2℃.

[0020] Preferably, the thin-film pressure sensor has two sets, each set including 7 sensors;

[0021] The first group of thin-film pressure sensors are embedded in the bottom of the upper left mold block cap, the waist of the upper left mold block cap, the R-corner of the upper left mold block, the top of the middle mold block cap, the R-corner of the upper right mold block, the waist of the upper right mold block cap, and the bottom of the upper right mold block cap. The seven thin-film pressure sensors are coaxially arranged and symmetrically distributed.

[0022] The second group of thin-film pressure sensors are sequentially embedded in the bottom of the lower left mold block cap, the R-corner of the lower left mold block, the waist of the lower left mold block cap, the top of the middle lower mold block cap, the waist of the lower right mold block cap, the R-corner of the lower right mold block, and the bottom of the lower right mold block cap. The seven thin-film pressure sensors are coaxially arranged and symmetrically distributed.

[0023] The range of each of the aforementioned thin-film pressure sensors is 10 MPa, and the data acquisition frequency is 20~50 Hz.

[0024] Secondly, the present invention provides a preforming method using the carbon fiber composite hat-shaped stringer preforming system described in the first aspect, as follows:

[0025] S1: The temperature of the hot molding die is controlled by the temperature controller system to reach the working temperature and kept at the working temperature for ≥10 minutes, so that the temperature difference between the embedded first thermocouple, second thermocouple and third thermocouple is ≤±2℃.

[0026] S2: Fix the prepreg layer to the upper surface of the lower mold block assembly using several positioning pins. Then, move the upper mold block assembly downwards through the displacement control system until it contacts the upper surface of the prepreg layer. During this process, observe the pressure value measured by the diaphragm pressure sensor located at the top of the upper mold block cap. When it reaches 0.01 MPa, stop moving the upper mold block assembly. At this time, the hot molding die is in the initial position. Keep it in the initial position for at least 5 minutes to allow the internal temperature of the prepreg layer to match the temperature of the hot molding die.

[0027] S3: Set the pressing rate to 0.1-20 mm / min and the pressing displacement to 0-30 mm in the displacement control system; then start the molding process, use the displacement control system to drive the upper mold block assembly to move downward and cooperate with the lower mold block assembly to jointly apply pressure to the prepreg layer, and record the pressure data of each point in real time through the distributed pressure sensor network.

[0028] S4: After the displacement control system drives the upper mold block assembly to the preset pressing displacement, the heat preservation program is started. After the working temperature is maintained for 20~60 minutes, the mold temperature controller system starts the cooling process. After the temperature drops to 28±1℃, the stringer preform is taken out from the hot molding special mold.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] By integrating a dedicated hot molding die, a mold temperature control system, a distributed pressure sensing network, and a displacement control system, the system can precisely control the interruption of the molding process at preset process nodes, achieving high-precision fabrication of carbon fiber composite cap-shaped stringers. At the same time, the system supports high-pressure molding conditions and is applicable to the preforming process of various materials such as thermosetting / thermoplastic prepregs and dry fiber cloth, and has a wide range of engineering applicability. Attached Figure Description

[0031] Figure 1 This is a structural block diagram of a carbon fiber composite hat-shaped stringer preforming system;

[0032] Figure 2 This is a structural diagram of a special mold for hot molding;

[0033] Figure 3 This is a schematic diagram of a mold temperature controller system used for temperature regulation;

[0034] Figure 4 This is a schematic diagram showing the location of the locating pin assembly;

[0035] Figure 5 This is a top view of the distribution location of the pressure sensing network used to monitor the pressure distribution during the preparation process;

[0036] Figure 6 for Figure 2 Perspective side view of the initial hot pressing moment of a special hot-pressing mold for medium-temperature molding;

[0037] Figure 7 A sample of a hat-shaped stringer prepared using the preforming system of this invention;

[0038] The attached diagram is labeled as follows: 1. Hot molding die; 2. Mold temperature control system; 3. Distributed pressure sensor network; 4. Displacement control system; 5. Lower support die assembly 1-1; 6. Upper support die assembly 1-2; 7. Lower pressure plate 1-3; 8. Upper pressure plate 1-4; 9. Water pipe assembly 1-5; 10. First water pipe 1-5-1; 11. Second water pipe 1-5-2; 12. Third water pipe 1-5-3; 13. Fourth water pipe 1-5-4; 14. Lower right die block 1-6; 15. Middle lower die block 1-7; 16. Lower left die block 1-8; 17. Upper right die block 1-9; 18. Middle upper die block 1-10; 19. Upper left die block 1-11; 10. First locating pin 1-12; 11. Second locating pin 1-13; 12. Third locating pin 1-14; 13. Fourth locating pin 1-15; 14. Fifth locating pin 1-16; 15. Sixth locating pin 1-17; 16. First thermocouple 1-18; 17. Second thermocouple 1-19; 18. Third thermocouple 1-20; 19. Cold medium inlet 2-1; 10. Cold medium. 2-2 outlet, 2-3 heat medium inlet, 2-4 heat medium outlet, 2-5 filter, 2-6 heating pump, 2-7 cooling solenoid valve, 2-8 temperature probe, 2-9 electrical control box, 2-10 frame, 2-11 heater, 3-1 first diaphragm pressure sensor, 3-2 second diaphragm pressure sensor, 3-3 third diaphragm pressure sensor, 3-4 fourth diaphragm pressure sensor, 3-5 fifth diaphragm pressure sensor, 3-6 sixth diaphragm pressure sensor, 3-7 seventh diaphragm pressure sensor, 3-8 eighth diaphragm pressure sensor, 3-9 ninth diaphragm pressure sensor, 3-10 tenth diaphragm pressure sensor, 3-11 eleventh diaphragm pressure sensor, 3-12 twelfth diaphragm pressure sensor, 3-13 thirteenth diaphragm pressure sensor, 3-14 fourteenth diaphragm pressure sensor. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0040] like Figure 1As shown, this invention provides a carbon fiber composite cap-shaped stringer preforming system. The preforming system mainly includes a hot-molding mold 1, a mold temperature control system 2, a distributed pressure sensing network 3, and a displacement control system 4. The mold temperature control system 2 regulates the temperature of the hot-molding mold 1, the distributed pressure sensing network 3 monitors the pressure distribution of the hot-molding mold 1 during the preparation process, and the displacement control system 4 precisely controls the downward displacement of the mold. This invention's preforming system offers high displacement control accuracy and is suitable not only for molding thermosetting carbon fiber reinforced resin-based prepregs but also for preforming high-modulus thermoplastic carbon fiber reinforced resin-based prepregs and dry fiber cloths.

[0041] The structure and connection methods of each part will be explained in detail below.

[0042] In the preforming system of the present invention, such as Figure 2 As shown, the hot molding die 1 mainly includes a lower support die assembly 1-1 and an upper support die assembly 1-2. Both the lower support die assembly 1-1 and the upper support die assembly 1-2 have channels through which heat exchange medium can pass, and the channels are connected to the mold temperature control system 2 through water pipe assembly 1-5. The mold temperature control system 2 is used to regulate the temperature of the prepreg layer.

[0043] As a preferred embodiment of the present invention, such as Figure 2 As shown, the water pipe assembly 1-5 mainly includes a first water pipe 1-5-1, a second water pipe 1-5-2, a third water pipe 1-5-3, and a fourth water pipe 1-5-4, all of which can be made of high-pressure resistant materials. One end of the first water pipe 1-5-1 is connected to the heat medium outlet 2-4 of the mold temperature controller system 2, and the other end is connected to the heat exchange channel inside the upper support mold assembly 1-2. One end of the second water pipe 1-5-2 is connected to the heat exchange channel inside the upper support mold assembly 1-2, and the other end is connected to the heat medium inlet 2-3 of the mold temperature controller system 2. The mold temperature controller system 2, through the first water pipe 1-5-1 and the second water pipe 1-5-2, forms a first heat exchange medium circuit with the upper support mold assembly 1-2, which heats the upper surface of the prepreg layer by heating the upper support mold assembly 1-2. Similarly, one end of the third water pipe 1-5-3 is connected to the heat medium outlet 2-4 of the mold temperature controller system 2, and the other end is connected to the heat exchange channel inside the lower support mold assembly 1-1. One end of the fourth water pipe 1-5-4 is connected to the heat exchange channel inside the lower support mold assembly 1-1, and the other end is connected to the heat medium inlet 2-3 of the mold temperature controller system 2. The mold temperature controller system 2, through the third water pipe 1-5-3 and the fourth water pipe 1-5-4, forms a second heat exchange medium circuit with the lower support mold assembly 1-1, which heats the lower surface of the prepreg layer by heating the lower support mold assembly 1-1. In other words, the mold temperature controller system 2, through the first and second heat exchange medium circuits, can uniformly control the temperature of both the upper and lower surfaces of the prepreg layer.

[0044] As a preferred embodiment of the present invention, such as Figure 3 As shown, the mold temperature control system 2 mainly includes a cold medium inlet 2-1, a cold medium outlet 2-2, a hot medium inlet 2-3, a hot medium outlet 2-4, a filter 2-5, a heating pump 2-6, a cooling solenoid valve 2-7, a temperature sensor 2-8, an electrical control box 2-9, a frame 2-10, and a heater 2-11. The filter 2-5, heating pump 2-6, cooling solenoid valve 2-7, temperature sensor 2-8, electrical control box 2-9, and heater 2-11 are all fixed to the frame 2-10. The cold medium inlet 2-1 is connected to the inlet of the heating pump 2-6 through a pipe containing the filter 2-5. The hot medium inlet 2-3 is also connected to the inlet of the heating pump 2-6 through a pipe. The outlet of the heating pump 2-6 is connected to the heater 2-11 through a pipe. Heater 2-11 is connected to heat medium outlet 2-4 via a pipe equipped with temperature sensor 2-8. Heat medium inlet 2-3 is also connected to cold medium outlet 2-2 via a pipe equipped with cooling solenoid valve 2-7. The heat transfer medium inside mold temperature controller system 2 can be water or oil, selected according to the required temperature range (e.g., water temperature ≤ 98℃, heat transfer oil temperature ≤ 400℃). Electrical control box 2-9 connects to the other components in mold temperature controller system 2 for data acquisition and feedback control. It employs a PID control algorithm with a temperature control accuracy of ±1℃, ensuring a temperature difference of ≤ ±2℃ on the surface of the prepreg layer.

[0045] In actual use (using water as the heat transfer medium), when the hot molding die 1 needs to be heated, the valves at the cold medium inlet 2-1, cold medium outlet 2-2, hot medium inlet 2-3, and hot medium outlet 2-4 are opened. Cooling water enters the heating pump 2-6 through the valve at the cold medium inlet 2-1, and is then heated by the heater 2-11. The heated water, reaching the preset temperature, is then fed back into the hot molding die 1 through the valve at the hot medium outlet 2-4. The hot medium inlet 2-3 is responsible for recovering the hot water that has passed through the hot molding die 1 after heat exchange and returning it to the heating pump 2-6 for secondary heating and reuse by the heater 2-11. During operation, if the temperature of the hot water heated by the heating pump 2-6, as measured by the temperature sensor 2-8, is higher than the preset temperature, a portion of the hot water is discharged from the valve at the cold medium outlet 2-2 to maintain a constant medium temperature within the mold temperature control system 2.

[0046] As a preferred embodiment of the present invention, the prepreg layer can be made of carbon fiber reinforced resin-based prepreg or dry fiber cloth with thermosetting or thermoplastic properties.

[0047] In the preforming system of the present invention, a lower pressure plate 1-3 is fixed to the lower side of the lower support mold assembly 1-1, and a lower mold block assembly is fixed to the upper side. An upper mold block assembly is fixed to the lower side of the upper support mold assembly 1-2, and an upper pressure plate 1-4 is fixed to the upper side. A prepreg layer is placed between the upper mold block assembly and the lower mold block assembly.

[0048] In a preferred embodiment of the present invention, the lower support mold assembly 1-1 is detachably connected to the lower pressure plate 1-3 and the lower mold block assembly via bolts, and the upper support mold assembly 1-2 is detachably connected to the upper mold block assembly and the upper pressure plate 1-4 via bolts. Furthermore, the upper pressure plate 1-4, upper support mold assembly 1-2, upper mold block assembly, prepreg layer, lower mold block assembly, lower support mold assembly 1-1, and lower pressure plate 1-3, stacked from top to bottom, are all coaxially arranged.

[0049] As a preferred embodiment of the present invention, such as Figures 4-6 As shown, the lower mold block assembly mainly includes the lower right mold block 1-6, the middle lower mold block 1-7, and the lower left mold block 1-8, which together form a central concave structure. The lower right mold block 1-6 and the lower left mold block 1-8 are fixed to the upper surface of the lower support mold assembly 1-1 by bolts, and the bottom of the middle lower mold block 1-7 is connected to the upper surface of the lower support mold assembly 1-1 by a spring that provides vertical elasticity. The upper mold block assembly includes the upper right mold block 1-9, the middle upper mold block 1-10, and the upper left mold block 1-11, which together form a central convex structure. The middle upper mold block 1-10 is fixed to the lower surface of the upper support mold assembly 1-2 by bolts, and the tops of the upper right mold block 1-9 and the upper left mold block 1-11 are respectively connected to the lower surface of the upper support mold assembly 1-2 by springs that provide vertical elasticity. The central concave structure and the central convex structure match, forming a mold space between them for constructing a cap-shaped stringer structure for the prepreg layer. In order for the spring to provide better vertical elastic force, the spring can be sleeved on the outside of the vertically fixed guide post, so that the spring can be compressed or rebound along the guide post.

[0050] When the hot molding die 1 is adjusted to the initial pressing position, the lower surfaces of the upper middle die block 1-10, the upper left die block 1-11, and the upper right die block 1-9 are basically on the same plane, and the upper surfaces of the lower middle die block 1-7, the lower right die block 1-6, and the lower left die block 1-8 are basically on the same plane. The distance between the two planes is the thickness of the prepreg layer. During the pressing process, the upper middle die block 1-10 moves downward under the action of the displacement control system, simultaneously pressing the prepreg layer and the lower middle die block 1-7 downward together. During the pressing process, the springs between the upper right die block 1-9 and the upper left die block 1-11 and the upper support die group 1-2 are gradually compressed, and the distance between them and the upper support die group gradually decreases. When the molding process is completed by pressing down to the preset distance, the springs between the upper right mold block 1-9 and the upper left mold block 1-11 and the upper support mold group 1-2 are compressed to their limits. At this time, these two mold blocks are in contact with the upper support mold group 1-2. At the same time, the spring between the middle and lower mold block 1-7 and the lower support mold group 1-1 is also compressed to its limits. At this time, the middle and lower mold block 1-7 and the lower support mold group 1-1 are also in contact with each other.

[0051] In practical use, such as Figure 4 As shown, the upper surface of the lower right mold block 1-6 is provided with a first positioning pin 1-12, a second positioning pin 1-13, and a third positioning pin 1-14, while the upper surface of the lower left mold block 1-8 is provided with a fourth positioning pin 1-15, a fifth positioning pin 1-16, and a sixth positioning pin 1-17. The two sets of positioning pins are symmetrically arranged. The second positioning pin 1-13 and the fifth positioning pin 1-16 are width positioning pins, responsible for controlling the width of the stringer preform; the first positioning pin 1-12, the third positioning pin 1-14, the fourth positioning pin 1-15, and the sixth positioning pin 1-17 are length positioning pins, responsible for controlling the axial length of the stringer preform. The diameter tolerance of each positioning pin is ±0.01mm, and the positioning accuracy is ±0.05mm.

[0052] In practical use, such as Figure 2 As shown, a first thermocouple 1-18 is horizontally embedded in the middle of the lower right mold block 1-6, a second thermocouple 1-19 is horizontally embedded in the middle of the lower left mold block 1-8, and a third thermocouple 1-20 is horizontally embedded in the middle of the upper middle mold block 1-10. The temperature monitoring range of all three thermocouples is 0~400℃, the temperature monitoring accuracy is ±1℃, and the embedding depth is ≥15mm.

[0053] In the preforming system of the present invention, such as Figure 2As shown, multiple vertical sliding shafts connect the upper support mold assembly 1-2 and the lower support mold assembly 1-1, allowing the upper support mold assembly 1-2 to slide up and down relative to the lower support mold assembly 1-1 along the sliding shafts. The upper pressure plate 1-4 and the lower pressure plate 1-3 are respectively connected to the displacement control system 4. The displacement control system 4 can control the downward displacement of the upper pressure plate 1-4 relative to the lower pressure plate 1-3, thereby driving the movement between the upper support mold assembly 1-2 and the lower support mold assembly 1-1, thus changing the vertical distance between the upper support mold assembly 1-2 and the lower support mold assembly 1-1.

[0054] As a preferred embodiment of the present invention, the displacement control system 4 can be a universal mechanical testing machine driven by a servo motor, used to automatically interrupt the molding process at a preset process node, with an interruption time resolution of ±0.1s, a displacement control accuracy of 0.001mm, a loading rate of 0.1-20mm / min, and a rated force of 250kN.

[0055] In the preforming system of the present invention, multiple thin-film pressure sensors are provided on one side of the upper mold block assembly and the lower mold block assembly that are in contact with the prepreg layer. All the thin-film pressure sensors together constitute a distributed pressure sensing network 3 for monitoring the pressure distribution on the prepreg layer during the preparation process.

[0056] In a preferred embodiment of the present invention, the thin-film pressure sensor has two sets, each set comprising seven sensors. For example... Figure 5As shown, the first group of thin-film pressure sensors are sequentially embedded in the bottom of the cap of the upper left mold block 1-11 (i.e., the eighth thin-film pressure sensor 3-8), the waist of the cap of the upper left mold block 1-11 (i.e., the ninth thin-film pressure sensor 3-9), the R-corner of the upper left mold block 1-11 (i.e., the tenth thin-film pressure sensor 3-10), the top of the cap of the upper middle mold block 1-10 (i.e., the eleventh thin-film pressure sensor 3-11), the R-corner of the upper right mold block 1-9 (i.e., the twelfth thin-film pressure sensor 3-12), the waist of the cap of the upper right mold block 1-9 (i.e., the thirteenth thin-film pressure sensor 3-13), and the bottom of the cap of the upper right mold block 1-9 (i.e., the fourteenth thin-film pressure sensor 3-14). The seven thin-film pressure sensors are coaxially arranged and symmetrically distributed. The second group of thin-film pressure sensors are sequentially embedded in the following locations: the bottom of the cap of the lower left mold block 1-8 (i.e., the first thin-film pressure sensor 3-1), the radius (R) of the lower left mold block 1-8 (i.e., the second thin-film pressure sensor 3-2), the waist of the cap of the lower left mold block 1-8 (i.e., the third thin-film pressure sensor 3-3), the top of the cap of the lower middle mold block 1-7 (i.e., the fourth thin-film pressure sensor 3-4), the waist of the cap of the lower right mold block 1-6 (i.e., the fifth thin-film pressure sensor 3-5), the radius (R) of the lower right mold block 1-6 (i.e., the sixth thin-film pressure sensor 3-6), and the bottom of the cap of the lower right mold block 1-6 (i.e., the seventh thin-film pressure sensor 3-7). Each thin-film pressure sensor has a range of 10 MPa and a data acquisition frequency of 20–50 Hz.

[0057] Utilizing the aforementioned carbon fiber composite hat-shaped stringer preforming system, this invention also provides a preforming method. This method involves controlling the temperature and mold pressing displacement, automatically interrupting the pressing process at a preset displacement node for heat preservation and shape retention, and then removing the preform from a dedicated mold after the heat preservation is complete, thus achieving the preparation of the hat-shaped stringer preform. The specific method is as follows:

[0058] S1: The temperature of the hot molding die 1 is controlled by the temperature controller system 2 to rise to the working temperature (30-400℃), and the temperature is maintained at the working temperature for ≥10min, so that the temperature difference between the embedded first thermocouple 1-18, second thermocouple 1-19 and third thermocouple 1-20 is ≤±2℃.

[0059] S2: The prepreg layer is fixed to the upper surface of the lower mold block assembly and positioned using multiple locating pins. Then, the upper mold block assembly is moved downwards by the displacement control system 4 until it contacts the upper surface of the prepreg layer. During this process, the pressure value measured by the thin-film pressure sensor located at the top of the cap of the upper mold block 1-10 is observed. When it reaches 0.01 MPa, the movement of the upper mold block assembly is stopped, and the hot molding die 1 is considered to be in the initial position. The temperature is maintained at the initial position for at least 5 minutes to ensure that the internal temperature of the prepreg layer is consistent with the temperature of the hot molding die 1.

[0060] S3: Set the pressing rate to 0.1-20 mm / min and the pressing displacement to 0-30 mm in the displacement control system 4. Then start the molding process, using the displacement control system 4 to drive the upper mold block assembly to move downward and cooperate with the lower mold block assembly to jointly apply pressure to the prepreg layer. The pressure data at each point is recorded in real time through the distributed pressure sensing network 3.

[0061] S4: After the displacement control system 4 drives the upper mold block assembly to the preset pressing displacement, the heat preservation program is started. After the working temperature is maintained for 20~60 minutes, the mold temperature controller system 2 starts the cooling process. After the temperature drops to 28±1℃, the stringer preform is taken out from the hot molding special mold 1.

[0062] In a preferred embodiment of the present invention, the pressing rate in step S3 is 2-6 mm / min.

[0063] In a preferred embodiment of the present invention, the heat preservation time in step S4 is 20 minutes.

[0064] This invention integrates a dedicated hot molding die, a high-precision mold temperature control device, a distributed pressure sensing network, and a displacement control system. By directly and precisely controlling the downward displacement, it effectively ensures the dimensional accuracy of the components. Simultaneously, the system supports high-pressure molding conditions and is applicable to preforming processes of various materials such as thermosetting / thermoplastic prepregs and dry fiber cloth, demonstrating broad engineering applicability.

[0065] Figure 7 The hot-molded hat-shaped stringer sample obtained using the preforming system of this invention is shown under the conditions of operating temperature 30℃, pressing rate 4mm / min, and pressing displacement 30mm. As can be seen from the figure, the sample surface is flat and wrinkle-free.

[0066] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A carbon fiber composite hat stringer preform system, characterized by, It comprises a hot die pressing special mold (1), a mold temperature machine system (2), a distributed pressure sensing network (3) and a displacement control system (4). The hot die pressing special mold (1) comprises a lower support mold group (1-1) and an upper support mold group (1-2); the lower side of the lower support mold group (1-1) is fixed with a lower pressing plate (1-3), and the upper side is fixed with a lower mold block assembly; the lower side of the upper support mold group (1-2) is fixed with an upper mold block assembly, and the upper side is fixed with an upper pressing plate (1-4); the upper mold block assembly and the lower mold block assembly are used for placing a prepreg laminate; a plurality of vertical sliding shafts are connected between the upper support mold group (1-2) and the lower support mold group (1-1), the upper pressing plate (1-4) and the lower pressing plate (1-3) are respectively connected with the displacement control system (4), the displacement control system (4) can control the downward displacement of the upper pressing plate (1-4) relative to the lower pressing plate (1-3), and the vertical distance between the upper support mold group (1-2) and the lower support mold group (1-1) can be changed; the upper support mold group (1-2) and the lower support mold group (1-1) are connected with the mold temperature machine system (2) for temperature regulation of the prepreg laminate through a water pipe assembly (1-5); one side of the upper mold block assembly and the lower mold block assembly in contact with the prepreg laminate is provided with a plurality of thin film pressure sensors, and all the thin film pressure sensors together constitute a distributed pressure sensing network (3) for monitoring the pressure distribution on the prepreg laminate during preparation; The lower mold block assembly comprises a right lower mold block (1-6), a middle lower mold block (1-7) and a left lower mold block (1-8), which together constitute a middle lower concave structure; the right lower mold block (1-6) and the left lower mold block (1-8) are fixed on the upper surface of the lower support mold group (1-1) by bolts, and the middle lower mold block (1-7) is connected with the upper surface of the lower support mold group (1-1) through springs which can provide vertical elastic force; the upper mold block assembly comprises a right upper mold block (1-9), a middle upper mold block (1-10) and a left upper mold block (1-11), which together constitute a middle lower convex structure; the middle upper mold block (1-10) is fixed on the lower surface of the upper support mold group (1-2) by bolts, and the top of the right upper mold block (1-9) and the left upper mold block (1-11) is respectively connected with the lower surface of the upper support mold group (1-2) through springs which can provide vertical elastic force; the middle lower concave structure and the middle lower convex structure are matched, and a mold space for forming a hat-shaped stringer structure of the prepreg laminate is formed between them; The thin film pressure sensor has two groups, each group comprising 7; The thin film pressure sensors of the first group are arranged in the left upper mold block (1-11) hat bottom, the left upper mold block (1-11) hat waist, the left upper mold block (1-11) R corner, the middle upper mold block (1-10) hat top, the right upper mold block (1-9) R corner, the right upper mold block (1-9) hat waist and the right upper mold block (1-9) hat bottom in turn, and the 7 thin film pressure sensors are coaxially arranged and symmetrically laid out. The second group of thin film pressure sensors are sequentially embedded in the bottom of the left lower mold block (1-8), the R corner of the left lower mold block (1-8), the waist of the left lower mold block (1-8), the top of the middle lower mold block (1-7), the waist of the right lower mold block (1-6), the R corner of the right lower mold block (1-6) and the bottom of the right lower mold block (1-6), and the seven thin film pressure sensors are coaxially arranged and symmetrically arranged.

2. A carbon fiber composite hat stringer preform system according to claim 1, wherein, A plurality of positioning pins for controlling the size of the prepreg laminate are symmetrically arranged on the right lower mold block (1-6) and the left lower mold block (1-8), respectively, each positioning pin has a diameter tolerance of ±0.01 mm and a positioning accuracy of ±0.05 mm.

3. A carbon fiber composite hat stringer preform system according to claim 1, wherein, The middle portions of the right lower mold block (1-6), the left lower mold block (1-8) and the middle upper mold block (1-10) are respectively horizontally embedded with a first thermocouple (1-18), a second thermocouple (1-19) and a third thermocouple (1-20); each thermocouple has a temperature monitoring range of 0-400℃, a temperature monitoring accuracy of ±1℃ and an embedding depth of ≥15 mm.

4. The carbon fiber composite hat stringer preform system of claim 1, wherein, The water pipe assembly (1-5) comprises a first water pipe (1-5-1), a second water pipe (1-5-2), a third water pipe (1-5-3) and a fourth water pipe (1-5-4). One end of the first water pipe (1-5-1) is connected with the hot medium outlet (2-4) of the mold temperature controller system (2), and the other end is connected with the upper support mold group (1-2); one end of the second water pipe (1-5-2) is connected with the upper support mold group (1-2), and the other end is connected with the hot medium inlet (2-3) of the mold temperature controller system (2); the mold temperature controller system (2) and the upper support mold group (1-2) form a first heat exchange medium circuit through the first water pipe (1-5-1) and the second water pipe (1-5-2). One end of the third water pipe (1-5-3) is connected with the hot medium outlet (2-4) of the mold temperature controller system (2), and the other end is connected with the lower support mold group (1-1); one end of the fourth water pipe (1-5-4) is connected with the lower support mold group (1-1), and the other end is connected with the hot medium inlet (2-3) of the mold temperature controller system (2); the mold temperature controller system (2) and the lower support mold group (1-1) form a second heat exchange medium circuit through the third water pipe (1-5-3) and the fourth water pipe (1-5-4). The mold temperature controller system (2) uniformly controls the temperature of the upper and lower surfaces of the prepreg laminate through the first heat exchange medium circuit and the second heat exchange medium circuit.

5. A carbon fiber composite hat stringer preform system according to claim 1, wherein, The prepreg laminate is a thermosetting or thermoplastic carbon fiber reinforced resin-based prepreg or dry fiber cloth.

6. A carbon fiber composite hat stringer preform system according to claim 1, wherein, The displacement control system (4) is a universal testing machine, which is used to automatically interrupt the mold pressing process at a preset process node, the interruption time resolution is ±0.1s, the displacement control accuracy is 0.001mm, the loading rate is 0.1-20mm / min, and the rated force value is 250kN.

7. A carbon fiber composite hat stringer preform system according to claim 1, wherein, The mold temperature controller system (2) comprises a filter (2-5), a heating pump (2-6), a cooling electromagnetic valve (2-7), a temperature sensing probe (2-8), an electrical control box (2-9) and a heater (2-11) fixed on a rack (2-10); the inlet of the heating pump (2-6) is connected with the cold medium inlet (2-1) and the hot medium inlet (2-3) through pipelines respectively, and the outlet is connected with the heater (2-11); a filter (2-5) is arranged on the pipeline at the cold medium inlet (2-1); the heater (2-11) is connected with the hot medium outlet (2-4) through a pipeline provided with the temperature sensing probe (2-8), and the hot medium inlet (2-3) is also connected with the cold medium outlet (2-2) through a pipeline provided with the cooling electromagnetic valve (2-7); The heat transfer medium in the mold temperature controller system (2) is water or oil; the electrical control box (2-9) adopts a PID control algorithm, and the temperature control precision is ±1℃, so that the temperature difference on the surface of the prepreg laminate is ≤±2℃.

8. A carbon fiber composite hat stringer preform system according to claim 1, wherein, The range of each thin film pressure sensor is 10MPa, and the data acquisition frequency is 20-50Hz.

9. A preforming method using the preform system of the hat stringer preform of any one of claims 1 to 8, characterized in that, Specifically as follows: S1: the temperature of the hot mold pressing special mold (1) is raised to the working temperature by the mold temperature controller system (2), and the temperature difference between the first thermocouple (1-18), the second thermocouple (1-19) and the third thermocouple (1-20) is ≤±2℃ at the working temperature for ≥10min; S2: the prepreg laminate is fixed on the upper surface of the lower mold block assembly through a plurality of positioning pins, and then the upper mold block assembly is driven to move downward to contact the upper surface of the prepreg laminate by the displacement control system (4); in the process, the pressure value measured by the thin film pressure sensor located at the top of the middle upper mold block (1-10) is observed, and when the pressure value reaches 0.01MPa, the movement of the upper mold block assembly is stopped, and at this time, the hot mold pressing special mold (1) is in the initial position; the temperature inside the prepreg laminate reaches the same temperature as the hot mold pressing special mold (1) at the initial position for at least 5min; S3: the displacement control system (4) is set to have a pressing rate of 0.1-20mm / min and a pressing displacement of 0-30mm; then the mold pressing process is started, the upper mold block assembly is driven to move downward by the displacement control system (4) and cooperates with the lower mold block assembly to apply pressure to the prepreg laminate, and the pressure data of each point are recorded in real time by the distributed pressure sensor network (3); S4: after the upper mold block assembly driven by the displacement control system (4) reaches the preset pressing displacement, the temperature maintaining program is started, and after the prepreg laminate is maintained at the working temperature for 20-60min, the mold temperature controller system (2) starts the cooling process, and the long string preform is taken out from the hot mold pressing special mold (1) when the temperature drops to 28±1℃.

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