A method for forming and processing H-beams of composite materials with clean edges

Abstract

The application relates to the technical field of composite material manufacturing, and discloses a net edge forming processing method of a composite material H-shaped beam. The device comprises a lower die, an upper die and a plurality of detachable metal blocks arranged at the edge of the lower die; the lower die is matched with the detachable metal blocks to form a rigid closed cavity matched with the net size of the H-shaped beam, and a temperature-resistant silica gel sealing strip is arranged at the joint of the two to prevent resin overflow. The method comprises the following steps: laying a prepreg with a small amount of process allowance on the lower die; fixing the metal blocks to the lower die through fasteners to form a closed cavity; integrally heat-pressing and curing; and after curing, firstly, the metal blocks are disassembled, and then, the mold is demolded. The application solves the technical problems of traditional H-shaped beam open mold forming needing secondary processing, low material utilization rate, edge fiber damage and the whole closed mold being unable to be demolded, and can one-time form the H-shaped beam with the net size and high precision.

Description

Technical Field

[0001] This invention relates to the field of composite material manufacturing technology, specifically to a method for forming and processing H-shaped beams of composite materials with clean edges. Background Technology

[0002] Composite H-beams have been widely used in aerospace, rail transportation and high-end equipment fields due to their high specific strength, high specific modulus and lightweight properties.

[0003] Currently, the fabrication of composite H-beams mainly employs autoclave molding, a process that typically involves prepreg layup in an open mold, followed by sealing with vacuum bags or other auxiliary materials and curing in an autoclave. However, this traditional open-mold molding method has inherent technical drawbacks. During curing, due to the lack of effective restraint at the mold edges, the fluid matrix resin under high temperature and pressure can carry fibers out of the mold cavity, resulting in numerous irregular resin burrs and excess fiber on the edges of the molded parts.

[0004] To obtain the final net dimensions, the cured blank must undergo subsequent machining. This post-processing step is not only complex and time-consuming, typically accounting for more than 30% of the overall manufacturing time and significantly reducing production efficiency, but the cutting process also severs continuous reinforcing fibers at the edges of the part, disrupting fiber integrity and stress transmission paths, thus adversely affecting the mechanical properties of the part. Furthermore, due to the lack of precise rigid boundary definition during curing, the part is prone to curing deformation, making it difficult to guarantee final dimensional accuracy, especially in critical areas such as the junction of the web and flange, where contour deviations often exceed 0.5 mm, failing to meet the precision assembly requirements of high-performance equipment.

[0005] Therefore, this invention proposes a method for forming and processing H-shaped beams of composite materials with clean edges to address the shortcomings of existing technologies. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for forming clean edges of composite H-beams, which solves the problems of burrs on the edges after curing, the need for secondary cutting, difficulty in controlling dimensional accuracy, and high material loss rate in the forming process of composite H-beams.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The first aspect of this invention provides a method for forming the clean edge of a composite H-beam, the method comprising the following steps:

[0009] S1. Laying and positioning: The pre-cut carbon fiber prepreg with a process allowance is laid in the lower mold coated with a release agent and positioned by positioning pins pre-set on the lower mold.

[0010] S2. Cleaning edge tooling assembly: Install a detachable metal block on the edge of the lower mold. The detachable metal block is embedded with a heat-resistant silicone sealing strip and is fastened to the lower mold by countersunk bolts to form a closed cavity.

[0011] S3, Integrated hot press curing: The assembled mold is placed in a hot press tank for staged pressure and temperature coupled curing.

[0012] S4. Cooling and Demolding: After curing, cool the mold, remove the detachable metal blocks, and then remove the formed composite material H-beam from the lower mold.

[0013] In one specific implementation, in step S1, the cutting of the carbon fiber prepreg leaves a process allowance of 2.0 mm or 2.1 mm outside the net dimension edge of the part.

[0014] In one specific implementation, the release agent in step S1 is a 3.8% (w / w) aqueous solution of polyvinyl alcohol. This release agent is prepared by dissolving polyvinyl alcohol and deionized water at 85–95°C for 1.5–2.5 hours.

[0015] As a specific implementation method, before step S2, a pre-compaction step is also included: covering the mold after layup with a vacuum bag, applying a vacuum pressure of -0.09MPa, and pre-compacting for 40 minutes to remove trapped air between the layups.

[0016] In one specific embodiment, the temperature resistance of the heat-resistant silicone sealing strip in step S2 is ≥230℃. This heat-resistant silicone sealing strip is prepared from the following components in parts by mass:

[0017] 100 parts of hydroxyl-terminated polydimethylsiloxane, 18 parts of fumed silica, 4 parts of tetraethyl orthosilicate, and 0.2 parts of dibutyltin dilaurate.

[0018] The specific preparation method of the heat-resistant silicone sealing strip includes:

[0019] The base adhesive is prepared by vacuum kneading hydroxyl-terminated polydimethylsiloxane with fumed silica at 145–155 °C for 60–90 minutes.

[0020] Cool the base adhesive to room temperature, add tetraethyl orthosilicate and dibutyltin dilaurate, stir under vacuum for 15-25 minutes, mix evenly, and then extrude to form.

[0021] The molded rubber strips are vulcanized at room temperature for 20-28 hours, and then placed in an oven for phased heating post-treatment. The post-treatment procedure is to keep the temperature at 150℃ for 2 hours, and then raise the temperature to 200℃ and keep it for 4 hours.

[0022] In one specific implementation, in step S2, when the detachable metal block is fastened to the lower mold by the countersunk bolt, the applied torque is 15 to 20 N·m to ensure the structural stability of the closed cavity during the subsequent pressurization process.

[0023] As a specific implementation method, the staged pressure-temperature coupled curing process described in step S3 has the following process parameters:

[0024] Heat to 80±5℃ and pressurize to 5.0±0.5MPa;

[0025] Continue heating to 130±5℃ and increasing the pressure to 10.0±0.5MPa;

[0026] The temperature is then raised to 180±5℃ and kept constant.

[0027] As a more specific implementation method, the specific process parameters in step S3 are as follows: heat up to 80±5℃ at a rate of 1.0±0.2℃ / min; continue to heat up to 130±5℃ and hold for 30±5 minutes; then heat up to 180±5℃ at a rate of 2.0±0.2℃ / min and hold at a constant temperature for 120±10 minutes.

[0028] In one specific implementation, in step S4, the mold is cooled to 55°C before the demolding operation is performed.

[0029] A second aspect of the present invention provides a composite material H-beam edge-forming apparatus for implementing the above-described method. The apparatus includes a lower mold, a plurality of detachable metal blocks disposed on the edge of the lower mold, and a plurality of countersunk bolts for fastening the detachable metal blocks to the lower mold. The lower mold is provided with positioning pins. The detachable metal blocks are provided with grooves, and heat-resistant silicone sealing strips are embedded in the grooves.

[0030] In one specific implementation, both the lower mold and the detachable metal block are made of INVAR steel.

[0031] This invention provides a method for forming the clean edge of a composite material H-beam. It has the following beneficial effects:

[0032] 1. This technical solution uses a combination of a lower mold and detachable metal blocks to form a rigid, closed cavity. During the thermosetting curing process, the embedded heat-resistant silicone sealing strip effectively prevents resin overflow, allowing the edge contour of the composite material to be directly defined by the high-precision inner wall of the mold. Therefore, the molded parts have smooth and complete edges, eliminating the need for traditional secondary machining processes such as cutting and grinding.

[0033] 2. This technical solution incorporates locating pins on the lower mold to ensure the precise initial position of the carbon fiber prepreg during the layup stage. Subsequently, detachable metal blocks secured with countersunk bolts are used to close and limit the prepreg in place, further preventing fiber slippage or misalignment during the high-temperature, high-pressure curing process. The synergistic effect of the locating pins and the metal blocks guarantees the geometric and positional accuracy of the final molded parts, especially at critical joints.

[0034] 3. Because this technical solution achieves one-time clean edge forming of parts, it completely eliminates time-consuming and labor-intensive post-processing steps, thereby significantly shortening the overall manufacturing cycle of the product and improving production efficiency. At the same time, since there is no need to reserve a large amount of cutting allowance, only a small amount of process allowance is required, which greatly reduces the waste of carbon fiber prepreg during the curing process, resulting in a significant improvement in the utilization rate of raw materials.

[0035] 4. Traditional machining processes inevitably sever carbon fibers at the edges of parts, causing fiber damage and stress concentration points, thus weakening their mechanical properties. This technical solution, through in-mold direct molding, ensures the continuity and integrity of carbon fibers at the edges of parts. These continuous fibers, undamaged by cutting, can more effectively transfer loads, thereby improving the overall structural integrity of the part and enhancing mechanical properties, including interlaminar shear strength. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the preparation process of the present invention;

[0037] Figure 2 This is a schematic diagram of the composite material H-beam edge-forming and processing device of the present invention;

[0038] Figure 3 This is a schematic diagram of the composite material H-beam edge-forming and processing device of the present invention.

[0039] Figure 4 This is a cross-sectional view of the composite material H-beam edge-forming and processing device of the present invention;

[0040] Figure 5 This is a schematic diagram of the performance test results of the present invention;

[0041] Figure 6This is a schematic diagram illustrating the effect of the fastening torque on the molding quality according to the present invention;

[0042] Figure 7 This is a schematic diagram illustrating the effect of the process allowance on the molding quality of the present invention.

[0043] Among them, 1. Hard cover plate one; 2. Hard cover plate two; 3. Lower mold; 4. H-beam; 5. Countersunk bolt; 6. Upper mold; 7. High-temperature resistant silicone sealing strip; 8. Positioning pin. Detailed Implementation

[0044] The technical solutions in 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.

[0045] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0046] T700 grade carbon fiber / epoxy resin unidirectional prepreg: fiber areal density 150g / m 2 Resin content 35%;

[0047] Its main components are: T700 grade carbon fiber; bisphenol A type epoxy resin, CAS No.: 1675-54-3; diaminodiphenyl sulfone, CAS No.: 80-08-0.

[0048] INVAR steel: grade 4J36.

[0049] Hydroxyl-terminated polydimethylsiloxane: CAS No.: 70131-67-8; viscosity at 25℃ is 5000-8000 mPa·s.

[0050] Fumed silica: CAS No.: 112945-52-5; specific surface area: 180-220 m² 2 / g.

[0051] Ethyl orthosilicate: CAS No.: 78-10-4; analytical grade.

[0052] Dibutyltin dilaurate: CAS No.: 77-58-7; analytical grade.

[0053] Polyvinyl alcohol (PVA): CAS No.: 9002-89-5.

[0054] Reference Figures 2-4The present invention provides a composite material H-beam edge-forming processing device, which includes a lower mold 3, a hard cover plate 1, a hard cover plate 2, a countersunk bolt 5, an upper mold 6, a heat-resistant silicone sealing strip 7, and a positioning pin 8.

[0055] The lower mold 3 is used to support the carbon fiber prepreg, and its cavity surface defines the main outer contour of the composite H-beam 4. The lower mold 3 is provided with positioning pins 8, which are used to initially position the prepreg during the layup process to ensure the accuracy of the layup position.

[0056] Hard cover plate 1 and hard cover plate 2 are detachable metal blocks installed on the edge of the lower mold 3; their inner surfaces together with the cavity surface of the lower mold 3 form a closed rigid cavity that matches the net size of the composite material H-beam 4.

[0057] The hard cover plate 1 and the hard cover plate 2 are provided with grooves, and the grooves are embedded with heat-resistant silicone sealing strips 7. The heat-resistant silicone sealing strips 7 are located at the joint surface between the hard cover plate and the lower mold 3. Their function is to fill the tiny gaps in the joint surface through elastic deformation during the hot pressing process, so as to prevent the matrix resin from overflowing.

[0058] The countersunk bolt 5 passes through the through holes on the first hard cover plate 1 and the second hard cover plate 2, and engages with the threaded hole on the lower mold 3 to provide a fastening force, so as to stably fix the hard cover plate on the lower mold 3 and ensure that the mold does not deform under high temperature and high pressure.

[0059] The upper mold 6 covers the assembled lower mold 3 and hard cover plate to seal the entire mold system and uniformly transmit pressure to the plywood in the autoclave.

[0060] The materials for the lower mold 3, hard cover plate 1, and hard cover plate 2 are all INVAR steel.

[0061] Preparation of heat-resistant silicone sealing strips:

[0062] Raw materials: hydroxyl-terminated polydimethylsiloxane, fumed silica, tetraethyl orthosilicate, dibutyltin dilaurate.

[0063] Preparation steps:

[0064] S1. Place 100 parts by weight of hydroxyl-terminated polydimethylsiloxane and 18 parts by weight of fumed silica in a kneader and knead for 75 minutes at 150°C and vacuum degree ≤-0.09MPa to obtain the base glue, and cool it for later use.

[0065] S2. Take 100 parts by weight of base adhesive, add 4 parts by weight of tetraethyl orthosilicate and 0.2 parts by weight of dibutyltin dilaurate, and stir in a vacuum planetary mixer for 20 minutes until evenly mixed;

[0066] S3. The uniformly mixed rubber compound is extruded through an extruder to form a rubber strip with a predetermined cross-sectional shape;

[0067] S4. Curl the extruded rubber strip at room temperature for 24 hours to allow it to initially solidify and set.

[0068] S5. Place the pre-cured adhesive strip in an oven and keep it at 150°C for 2 hours, then raise the temperature to 200°C and keep it at 200°C for 4 hours. After finishing the process, the finished product is obtained.

[0069] Preparation of water-based release agent:

[0070] Raw materials: Polyvinyl alcohol (PVA), deionized water;

[0071] Preparation steps: Slowly add 4 parts by weight of polyvinyl alcohol to 100 parts by weight of deionized water heated to 90°C. Continue stirring at this temperature for 2 hours until the polyvinyl alcohol is completely dissolved, forming a homogeneous and transparent solution. After cooling, a release agent product with a mass percentage concentration of approximately 3.8% is obtained.

[0072] Examples 1-3: Example 1:

[0073] See attached document Figure 1 As shown in the figure, this embodiment provides a method for forming the clean edge of a composite material H-beam, and the specific steps are as follows:

[0074] S1. Lamination and Positioning: Clean the INVAR steel molding device and uniformly spray the aforementioned water-based release agent onto the cavity surface of the lower mold 3; use a CNC cutting machine to cut T700 grade carbon fiber / epoxy resin unidirectional prepreg, leaving a 2.0mm process allowance on the outer side of the net dimension edge of the part.

[0075] Next, the cut prepreg is laid in the lower mold 3 according to the layup sequence and direction requirements, and is precisely positioned by the positioning pins 8 on the lower mold 3.

[0076] In this embodiment, after all the layers are laid, a preferred pre-compaction step is included: a vacuum bag is placed over the layer body, a vacuum pressure of -0.09 MPa is applied, and pre-compaction is performed at room temperature for 40 minutes to remove trapped air between the layers.

[0077] S2. Cleaning tooling assembly: Remove the vacuum bag and install the hard cover plate 1 and hard cover plate 2, which are embedded with the heat-resistant silicone sealing strip 7 prepared above, on the edge of the lower mold 3; use a torque wrench to tighten the countersunk bolts 5 one by one, and apply a final tightening torque of 18 N·m to form a closed cavity.

[0078] S3, Integrated Hot Press Curing: Place the assembled mold into the hot press tank, close the tank door and start the curing process;

[0079] The curing process parameters are as follows:

[0080] The temperature was increased to 80℃ at a heating rate of 1.0℃ / min, while the pressure was increased to 5.0MPa.

[0081] Continue heating to 130℃ and maintain this temperature for 30 minutes, while simultaneously increasing the pressure inside the tank to 10.0 MPa;

[0082] Then raise the temperature to 180℃ at a rate of 2.0℃ / min and hold at this temperature for 120 minutes.

[0083] S4. Cooling and Demolding: After the curing process is completed, cool the mold with the furnace. After the mold temperature drops to 55°C, open the autoclave door and remove the mold; first, loosen and remove all countersunk bolts 5 in sequence, and remove hard cover plate 1 and hard cover plate 2; then, use a demolding tool to completely remove the molded composite material H-beam 4 from the lower mold 3. Example 2:

[0084] The processing method in this embodiment is basically the same as that in Embodiment 1, except that the process parameters for integrated hot pressing curing in step S3 are adjusted as follows:

[0085] The temperature was increased to 75℃ at a heating rate of 1.2℃ / min, while the pressure was increased to 4.5MPa.

[0086] Continue heating to 125℃ and maintain this temperature for 35 minutes, while simultaneously increasing the pressure inside the tank to 9.5MPa;

[0087] Then, increase the temperature to 175℃ at a heating rate of 2.2℃ / min, and hold at this temperature for 130 minutes. Example 3:

[0088] The processing method in this embodiment is basically the same as that in Embodiment 1, except that:

[0089] In step S1, the reserved process allowance is 2.1mm.

[0090] In step S2, the final tightening torque applied is 20 N·m.

[0091] The process parameters for step S3, integrated hot-press curing, are adjusted as follows:

[0092] The temperature was increased to 85℃ at a heating rate of 0.8℃ / min, while the pressure was increased to 5.5MPa.

[0093] Continue heating to 135℃ and hold at this temperature for 25 minutes, while simultaneously increasing the pressure inside the tank to 10.5MPa;

[0094] Then, increase the temperature to 185℃ at a rate of 1.8℃ / min and hold at this temperature for 110 minutes.

[0095] Comparative Examples 1-3:

[0096] Comparative Example 1: Traditional mold-making process

[0097] The processing method of this comparative example is basically the same as that of Example 1, except that: instead of using detachable metal blocks, heat-resistant silicone sealing strips, and an upper mold, an open mold is used, and vacuum bags and other auxiliary materials are directly covered on top of the layup for hot pressing and curing. After curing and demolding, the edges of the parts have a large number of resin burrs and irregular fibers, which require subsequent cutting processing using a five-axis CNC machine tool to achieve the final dimensions.

[0098] Comparative Example 2: Using flexible edge-stop technology

[0099] The processing method of this comparative example is basically the same as that of Example 1, except that the rigid, detachable metal blocks 1 and 2 are replaced with high-temperature resistant silicone sheets as edge-blocking materials. After curing and demolding, the edges of the parts exhibit rounded corners and outward convexity due to the elastic deformation of the silicone sheet under high temperature and pressure, failing to form clear net dimensional edges.

[0100] Comparative Example 3: Using a non-removable integral mold

[0101] The processing method of this comparative example is basically the same as that of Example 1, except that the lower mold 3 and the detachable metal blocks 1 and 2 are designed as an integral, non-separable, closed mold. After curing, the concave geometry of the composite material H-beam 4 forms an undercut, causing the part to be unable to be removed from the integral mold, resulting in demolding failure.

[0102] Test Example 1-3:

[0103] The following performance tests were performed on the samples obtained in Examples 1-3 and Comparative Examples 1-2 (no sample was obtained for Comparative Example 3 because it could not be demolded).

[0104] Test Example 1: Comprehensive Test of Physical and Mechanical Properties

[0105] Edge roughness test: This test is performed in accordance with GB / T-3505-2009 standard.

[0106] (1) Testing equipment: contact profilometer.

[0107] (2) Test Procedure: Fix the H-beam sample to be tested on the test platform. Randomly select five different locations as measurement points on the free edge of the flange of the part. At each measurement point, drive the instrument probe to slide along the direction perpendicular to the edge to collect samples, with a sampling length of 4 mm. The instrument automatically calculates and records the arithmetic mean deviation Ra value of the profile within this sampling length. The final result is the arithmetic mean of the Ra values ​​of the five measurement points.

[0108] Dimensional accuracy test:

[0109] (1) Testing equipment: coordinate measuring machine.

[0110] (2) Test steps: Fix the sample to be tested stably on the worktable of the coordinate measuring machine; use a high-precision probe to perform multi-point touch test on the joint between the web and the flange of the H-beam to obtain the actual three-dimensional coordinate data of the area; compare the collected data with the original three-dimensional model to calculate the actual misalignment of the two planes of the web and the flange at the joint.

[0111] Material utilization rate calculation:

[0112] (1) Testing equipment: an electronic balance with an accuracy of 0.01g.

[0113] (2) Calculation steps: First, record the total mass of prepreg consumed to manufacture a single H-beam; then, measure the net mass of the final molded part; the material utilization rate is calculated by the following formula: Material utilization rate (%) = (net mass of the final molded part / total mass of prepreg used) × 100%.

[0114] Interlaminar shear strength test: This test is performed in accordance with ASTM D2344 standard.

[0115] (1) Testing equipment: Universal testing machine.

[0116] (2) Test procedure: Cut a specimen with dimensions of 20mm×6mm×2mm from the straight section of the flange of the H-beam; place the specimen on the three-point bending fixture with a support span of 12mm; apply load at a loading rate of 1mm / min until the specimen fails due to interlaminar shear; record the maximum load value at failure and calculate the interlaminar shear strength according to the standard formula; test five valid data for each group of samples and take the arithmetic mean of the results.

[0117] Test results: The performance test results of each sample are shown in Table 1.

[0118] Table 1: Performance Test Results

[0119]

[0120] Results Analysis: From the appendix Figure 5As can be seen from the test results in Table 1, the composite H-beams prepared in Examples 1, 2, and 3 all exhibit consistent and good performance in terms of edge roughness, misalignment at joints, material utilization, and interlaminar shear strength.

[0121] The molding device provided by this technical solution forms a closed cavity that matches the final net size of the part through the rigid combination of the lower mold 3 and the hard cover plate 1 and the hard cover plate 2. During the curing process, the resin flow under high temperature and high pressure is restricted by the inner wall of the rigid cavity. At the same time, the heat-resistant silicone sealing strip 7 set at the joint undergoes elastic deformation under pressure, filling the tiny gap between the lower mold 3 and the hard cover plate, preventing the resin from overflowing to the outside of the mold. This structural combination directly results in the part edge being formed by the high-precision inner wall of the mold in one step, thereby obtaining the low edge roughness Ra value and low joint misalignment shown in Table 1.

[0122] This method eliminates the need for secondary cutting of parts by forming the prepreg within the mold. Therefore, it is not necessary to reserve a large amount of processing allowance during the raw material cutting stage, but only a small amount of process allowance is required, so that most of the prepreg material becomes an effective part of the final product. This reason is directly reflected in the material utilization data in Table 1. In addition, the detachable structure of the hard cover plate 1 and the hard cover plate 2 allows the undercut constraint formed by the concave geometry of the H-beam to be released after curing, so that the parts can be smoothly removed from the lower mold 3, solving the technical problem of demolding failure in Comparative Example 3 due to the use of an integral mold.

[0123] In traditional processes (such as Comparative Example 1), secondary cutting will sever the continuous carbon fibers at the edge of the part, causing fiber damage and structural discontinuity. This technical solution, through integrated thermoforming, allows the fibers at the edge of the part to maintain their original continuity during the molding process, without any cutting damage. These complete and continuous fiber structures can effectively transfer stress when subjected to loads; the interlaminar shear strength values ​​of Examples 1, 2, and 3 in Table 1 are higher than those of Comparative Example 1, which objectively reflects this structural integrity.

[0124] Test Example 2: Verification of the Influence of Tightening Torque on Molding Quality

[0125] This test case was set up to verify the effect of the tightening torque of the countersunk bolt 5 on the net edge forming quality of the composite H-beam.

[0126] (1) Test method:

[0127] Five sets of samples were prepared. Except for the final tightening torque of the countersunk bolt 5, which was set to 10 N·m, 15 N·m, 18 N·m, 20 N·m and 25 N·m respectively, all other preparation processes, equipment and raw materials were exactly the same as in Example 1.

[0128] (2) Performance testing:

[0129] For each H-beam sample prepared, the edge roughness Ra of the free edge of the flange and the misalignment at the junction of the web and the flange were tested according to the test steps in Test Example 1.

[0130] Test results: The performance test results of the samples under different tightening torques are shown in Table 2.

[0131] Table 2: Effect of fastening torque on molding quality

[0132]

[0133] Results Analysis: From the appendix Figure 6 The test data in Table 2 show that the tightening torque of the countersunk bolt 5 has a direct impact on the quality of the final molded part. When the tightening torque is 10 N·m, the edge roughness and misalignment at the joint of the sample are relatively high, and resin overflow is observed. When the tightening torque is in the range of 15 N·m to 20 N·m, the edge roughness and misalignment at the joint of the sample remain at a low level. When the tightening torque is increased to 25 N·m, no further improvement in the molding quality indicators is observed, and a risk of damage to the threaded hole is found when disassembling the mold.

[0134] Test Example 3: Verification of the Influence of Process Allowance on Molding Quality

[0135] This test case was designed to verify the effect of the process allowance reserved during prepreg cutting on the net edge forming quality of composite H-beams.

[0136] (1) Test method:

[0137] Five sets of samples were prepared. Except for the process allowance reserved outside the net size edge of the part in step (1) which was set to 1.0mm, 1.5mm, 2.0mm, 2.5mm and 3.0mm respectively, all other preparation processes, equipment and raw materials were exactly the same as in Example 1.

[0138] (2) Performance testing:

[0139] For each group of H-beam samples, the edge roughness Ra of the free edge of the flange and the material utilization rate were tested according to the test steps in Test Example 1. At the same time, the edges of the parts were visually inspected and recorded.

[0140] Test results: The performance test results of the samples under different process allowances are shown in Table 3.

[0141] Table 3: Influence of process allowance on molding quality

[0142]

[0143] Results Analysis: From the appendix Figure 7 The test data in Table 3 show that the process allowance of the prepreg has a direct impact on the quality of the final molded part. When the process allowance is 1.0 mm, the total amount of material is insufficient to completely fill the rigid closed cavity during hot pressing, resulting in missing glue defects at the edge of the part and a significant increase in edge roughness. When the process allowance is increased to 1.5 mm, the missing glue phenomenon is improved, but the ideal molding state is still not achieved. When the process allowance is in the range of 2.0 mm to 2.5 mm, the total amount of material can ensure that the cavity is completely filled and is directly limited by the inner wall of the mold, resulting in a smooth surface and a complete net size edge. When the process allowance is further increased to 3.0 mm, the edge quality of the part is not improved, but due to the increase in the total amount of raw materials and the unchanged net weight of the final part, the material utilization rate decreases significantly.

[0144] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method of net shape forming a composite H-beam, characterized by, The method comprises the following steps: S1, layering and positioning: cutting and reserving process allowance of carbon fiber prepreg in advance, laying in the lower mold coated with release agent, and positioning by positioning pins preset on the lower mold; S2, net edge tool assembly: installing detachable metal blocks on the edge of the lower mold, embedding temperature-resistant silicone sealing strips in the detachable metal blocks, and fastening the detachable metal blocks and the lower mold by means of countersunk bolts to form a closed cavity; S3, integrated hot pressing and curing: placing the assembled mold in a hot pressing tank for curing under the control of staged pressure and temperature coupling, and the process parameters are as follows: Rising to 80±5℃, and pressurizing to 5.0±0.5MPa; Continuing to rise to 130±5℃, and increasing the pressure to 10.0±0.5MPa; Rising to 180±5℃ again, and constant temperature holding; S4, cooling and demolding: after curing, cooling the mold, removing the detachable metal blocks, and taking out the formed composite H-shaped beam from the lower mold, In step S1, the cutting of the carbon fiber prepreg reserves a process allowance of 2.0mm or 2.1mm outside the net size edge of the part.

2. The method of claim 1, wherein, In step S1, the release agent is a polyvinyl alcohol aqueous solution with a mass percentage concentration of 3.8%.

3. The method of claim 1, wherein, Before step S2, a pre-compaction step is further included: Covering the layered mold with a vacuum bag and applying a vacuum pressure of-0.09MPa for pre-compaction for 40 minutes.

4. The method of claim 1, wherein, The temperature resistance of the temperature-resistant silicone sealing strip is ≥230℃.

5. The method of claim 4, wherein the H-beam is a composite H-beam. The temperature-resistant silicone sealing strip is prepared from the following components by mass fraction: Hydroxyl-terminated polydimethylsiloxane: 100 parts; Fumed silica: 18 parts; Tetraethyl orthosilicate: 4 parts; Dibutyltin dilaurate: 0.2 parts.

6. The method of claim 1, wherein, In step S2, when fastening the detachable metal blocks and the lower mold by means of the countersunk bolts, the applied torque is 15-20N·m.

7. The method of claim 1, wherein the H-beam is a composite H-beam. In step S3, the specific process parameters are as follows: Rising to 80±5℃ at a rate of 1.0±0.2℃ / min; After continuing to rise to 130±5℃, holding for 30±5 minutes; Rising to 180±5℃ at a rate of 2.0±0.2℃ / min, and constant temperature holding for 120±10 minutes.

8. The method of claim 1, wherein, In step S4, after cooling the mold to 55℃, the demolding operation is performed.

9. The method of claim 1, wherein, The materials of the lower mold and the detachable metal blocks are both INVAR steel.

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