Preparation process of needle core bed of warp knitting machine for high-pressure compression molding of carbon fiber composite material

Abstract

The invention relates to a preparation process of a needle core bed of a warp knitting machine for high-pressure compression molding of a carbon fiber composite material, and belongs to the technical field of carbon fiber composite material molding and textile machinery. Aiming at the problems that a traditional metal needle core bed is large in weight and high in thermal deformation and an existing carbon fiber mold pressing process is low in efficiency, multiple in defect, high in cost and the like, breakthrough is achieved through the following technical scheme that microwave-vibration synergistic curing is conducted, specifically, microwave frequency and vibration parameters are regulated and controlled in stages, dynamic pressure feedback is combined, the curing time is shortened to 60-90 min, and the porosity is smaller than or equal to 0.3%; according to material-mold collaborative design, plasma activated T700-grade prepreg and nano silicon dioxide modified resin are adopted, and the tensile strength reaches 5,000 MPa or above; the silicon carbide mold is coated with the multi-wall carbon nano tube sensitization layer and is matched with the conformal cooling runner, so that the service life of the mold is prolonged, and the anti-deformation structure is optimized. Efficient, high-precision and light-weight manufacturing of the needle core bed is achieved, the comprehensive cost is reduced, and key technical support is provided for upgrading of a high-speed warp knitting machine.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fiber composite material molding and textile machinery, in particular to a preparation process of a needle core bed of a warp knitting machine for high-pressure compression molding of carbon fiber composite materials. Background Art

[0002] The traditional metal warp knitting machine needle core bed is difficult to meet the lightweight and high-precision requirements of high-speed warp knitting machines due to its heavy weight, high thermal deformation, and easy corrosion. Carbon fiber composite material alternatives are limited by the low efficiency of traditional molding process (curing ≥ 2 hours), many defects (porosity ≥

[0003] Bottlenecks include poor mold adaptability (1.5%), poor mold adaptability (dimensional tolerance ±0.15mm), and high costs (mold life ≤ 2,000 cycles). Existing improved technologies, such as ultrasonic-assisted curing and split mold design, fail to address multi-stage coordinated control and surface homogenization, hindering the industrial application of carbon fiber warp knitting machine needle core beds.

[0004] Therefore, a preparation process for a high-pressure compression-molded carbon fiber composite warp knitting machine needle core bed is needed to solve the above problems. Summary of the Invention

[0005] In order to solve the problems of the prior art, the present invention provides a preparation process of a needle core bed of a warp knitting machine for high-pressure compression molding of carbon fiber composite materials.

[0006] In order to solve the above technical problems, the present invention is achieved through the following technical solutions: a preparation process for a high-pressure compression-molded carbon fiber composite warp knitting machine needle core bed, comprising the following steps:

[0007] S1: Prepreg selection and pretreatment: Select T700 grade carbon fiber prepreg, the prepreg resin matrix is ​​epoxy resin, and the resin content is controlled at 35-40wt%; the prepreg is subjected to plasma surface treatment with a treatment power of 150-200W and a treatment time of 30-60s to make the fiber surface contact angle ≤20°;

[0008] S2: Directed Lamination and Interlayer Compaction: Orthogonal lamination (0° / 90° alternating lamination) is designed based on the stress direction of the warp knitting machine needle core bed. After each layer is laid, a roller compactor is used to apply 0.5-1.0MPa pressure to eliminate interlayer bubbles. The interface bonding strength is ≥40MPa. The total number of layers is 20-30, and the fiber volume fraction is ≥60%.

[0009] S3: Mold pretreatment: The mold is preheated to 80-100°C, the mold surface roughness Ra is ≤ 0.8 μm, and a microwave-sensitive layer (polyimide coating containing 5-10 wt% multi-walled carbon nanotubes) is coated on the mold cavity surface;

[0010] S4: Microwave-vibration composite curing: After placing the laminate preform into the mold, apply in stages:

[0011] Stage 1: Microwave frequency 2.45 GHz, heating rate 3-5°C / min to 100-120°C, simultaneous application of high-frequency vibration (frequency 50-100 Hz, amplitude 0.05-0.1 mm), and step-by-step pressure increase to 5-8 MPa;

[0012] Stage 2: Reduce microwave power by 30%, increase temperature by 1-2°C / min to 180-200°C, apply low-frequency vibration (frequency 20-50 Hz, amplitude 0.1-0.3 mm), and hold pressure for 60-90 min.

[0013] S5: Gradient cooling and demoulding: After curing, the temperature is gradually lowered to below 50°C at a rate of ≤5°C / min. After demoulding, the surface of the warp knitting machine needle core bed is laser-finished. The dimensional tolerance is controlled at ±0.05mm and the surface roughness Ra≤0.4μm.

[0014] This application breaks through the bottleneck of low efficiency and poor precision of traditional molding process through the synergistic effect of rapid microwave heating and high-frequency vibration. After T700-grade carbon fiber prepreg is treated with plasma activation, orthogonal oriented plying (0° / 90° alternating) and roller compaction technology are used, combined with staged dynamic control of microwave power (2.45GHz) and vibration parameters (20-100Hz) to achieve uniform resin impregnation and high fiber densification, shorten the curing time to 60-90min, and increase the tensile strength to more than 5,000MPa. The innovatively designed mold is coated with a multi-walled carbon nanotube sensitization layer and equipped with a conformal cooling channel (±3℃ temperature control), so that the surface roughness of the warp knitting machine needle core bed reaches Ra≤0.4μm, and the dimensional accuracy is stable at ±0.05mm. At the same time, the mold life exceeds 10,000 times and energy consumption is reduced by 25%. The Z-shaped step surface connection structure (10-15 sections) and the epoxy film composite interface effectively compensate for thermal expansion differences, with deformation ≤0.02mm / m. This process combines the advantages of high efficiency, high precision and low cost, providing a disruptive solution for lightweight and high-performance textile machinery.

[0015] In one possible embodiment, a nano-silica modifier is added to the prepreg resin matrix in S1 in an amount of 0.5-1.0 wt %. After modification, the elongation at break of the resin matrix is ​​≥5%, and the interfacial shear strength is ≥45 MPa.

[0016] In one possible embodiment, high-frequency vibration and low-frequency vibration in S4 are applied in different areas, wherein high-frequency vibration is preferentially applied to the needle core bed slot area of ​​the warp knitting machine and low-frequency vibration is applied to the plane area, and the vibration acceleration gradient is 5-20g.

[0017] In one possible embodiment, the thickness of the microwave sensitizing layer is 50-100 μm, and the microwave absorption efficiency is increased by 40-60% compared with the uncoated mold. The mold is integrated with a conformal cooling channel with a diameter of 3-5 mm. The cooling medium is thermal oil, and the temperature control accuracy is ±3°C.

[0018] In one possible embodiment, the pressure control in step S4 adopts a dynamic feedback mechanism to adjust the pressure curve in real time according to the resin flow index. The matching relationship between the resin flow front speed and the vibration frequency is:

[0019] When the resin flow rate is ≤0.1mm / s, the vibration frequency is ≤30Hz;

[0020] When the resin flow rate is greater than 0.1 mm / s, the vibration frequency increases to 50-100 Hz.

[0021] In one possible embodiment, the segmented structural design of the warp knitting machine needle core bed is divided into 10-15 segments along the length direction. The segments are connected by Z-shaped step surfaces with an angle of 25-35° between the steps. The gap between the segments is 0.1-0.3mm, and the segments are connected by epoxy film (thickness 0.1-0.2mm) and titanium alloy screws.

[0022] The beneficial effects of the present invention are:

[0023] 1. This patent uses microwave vibration composite curing technology and material-mold collaborative design to achieve the following in the preparation of the needle core bed of the carbon fiber warp knitting machine: rapid microwave heating (2.45GHz) combined with staged vibration (high frequency 80Hz / low frequency 30Hz) shortens the curing time from 2 hours in the traditional process to 60-90min, reducing energy consumption by 25%; dynamic pressure feedback (5-8MPa) matches the resin flow rate (0.1-0.2mm / s) in real time, making the porosity ≤0.3% (traditional process ≥1.8%) and the interface shear strength increased to 45MPa.

[0024] 2. Breakthrough in mechanical properties: The synergistic effect of T700-grade carbon fiber orthogonal ply (0° / 90°) and nano-silica modification (0.8wt%) achieves a tensile strength of 5,120 MPa, a 240% increase over the metal warp knitting machine needle core bed (1,500 MPa); plasma pretreatment (contact angle ≤ 20°) increases resin wettability by 50% and increases the interfacial bonding strength to 48 MPa.

[0025] 3. Precision manufacturing and stability: The mold (surface Ra ≤ 0.8μm) and conformal cooling channel (±3°C temperature control) ensure that the dimensional tolerance of the warp knitting machine needle core bed is ≤ ±0.05mm; the segmented Z-shaped structure (10-15 segments) compensates for thermal expansion differences, with thermal deformation ≤0.02mm / m, 75% lower than that of metal materials. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] A preparation process for a high-pressure compression-molded carbon fiber composite warp knitting machine needle core bed.

[0028] Example 1, Preparation of warp knitting machine needle core bed under basic process parameters

[0029] Implementation steps

[0030] Prepreg treatment: T700 grade carbon fiber prepreg (epoxy resin content 38 wt%) was treated with argon plasma (power 180 W, time 40 s), and the contact angle was reduced to 18°.

[0031] Laying and compaction: 24 layers of 0° / 90° orthogonal laying, each layer is compacted with a 0.8MPa roller after laying, and the fiber volume fraction is 62%.

[0032] Mold configuration: The mold (surface Ra 0.6 μm) was coated with a sensitized layer (thickness 80 μm) containing 8 wt % multi-walled carbon nanotubes and preheated to 90°C.

[0033] Microwave vibration curing:

[0034] Stage 1: microwave frequency 2.45 GHz, heating rate 4°C / min to 110°C, simultaneous application of 80 Hz high-frequency vibration (amplitude 0.08 mm), and pressure increased to 7 MPa;

[0035] Stage 2: The microwave power was reduced to 70%, the heating rate was 1.5°C / min to 190°C, and the mixture was switched to 30 Hz low-frequency vibration (amplitude 0.2 mm) and maintained under pressure for 80 min.

[0036] Cooling and processing: Cooling to 45°C at 4°C / min. After laser finishing, the needle bed size of the warp knitting machine is 250×50×20mm.

[0037] Test results

[0038] index This embodiment Traditional autoclave process (comparative example) Tensile strength (MPa) 5,120 4,200 Porosity (%) 0.3 1.8 Surface roughness Ra (μm) 0.35 1.5 Dimensional tolerance (mm) ±0.03 ±0.12 Thermal deformation (mm / m) 0.015 0.08

[0039] Example 2: Vibration frequency gradient optimization

[0040] Vibration parameter comparison

[0041] Plan A: fixed frequency 50 Hz throughout (amplitude 0.1 mm);

[0042] Solution B (the present invention): regional vibration (80 Hz in the slot area, 30 Hz in the plane area, and 15 g acceleration gradient).

[0043] Result Analysis

[0044] parameter Option A (uniform vibration) Plan B (partitioned vibration) Slot filling completeness 92％ 99％ Interface shear strength 38MPa 45MPa Demolding force (kN) 12.5 8.2

[0045] Conclusion: Partitioned vibration significantly improves the molding quality of complex structures and reduces demoulding force by 34%.

[0046] Example 3: Nano-silica modified resin matrix.

[0047] Comparison of modifier addition amount,

[0048] Group 1: no nano-silica added;

[0049] Group 2: 0.8 wt% of nano-silica (particle size 20 nm) was added.

[0050] Performance testing:

[0051] index Group 1 Group 2 Interface shear strength (MPa) 36 48 Elongation at break (%) 3.2 5.8 Moisture and heat resistance (strength retention rate) 85％ 93％

[0052] Conclusion: Nano-modification improves the interface performance by 33% and enhances the moisture and heat resistance.

[0053] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing a needle core bed of a warp knitting machine for high-pressure compression molding of carbon fiber composite materials, characterized in that: The following steps are involved: S1: Prepreg selection and pretreatment: Select T700 grade carbon fiber prepreg, the prepreg resin matrix is ​​epoxy resin, and the resin content is controlled at 35-40wt%; the prepreg is subjected to plasma surface treatment with a treatment power of 150-200W and a treatment time of 30-60s to make the fiber surface contact angle ≤20°; S2: Directed Lamination and Interlayer Compaction: Orthogonal lamination (0° / 90° alternating lamination) is designed based on the stress direction of the warp knitting machine needle core bed. After each layer is laid, a roller compactor is used to apply 0.5-1.0MPa pressure to eliminate interlayer bubbles. The interface bonding strength is ≥40MPa. The total number of layers is 20-30, and the fiber volume fraction is ≥60%. S3: Mold pretreatment: The mold is preheated to 80-100°C, the mold surface roughness Ra is ≤ 0.8 μm, and a microwave-sensitive layer (polyimide coating containing 5-10 wt% multi-walled carbon nanotubes) is coated on the mold cavity surface; S4: Microwave-vibration composite curing: After placing the laminate preform into the mold, apply in stages: Stage 1: Microwave frequency 2.45 GHz, heating rate 3-5°C / min to 100-120°C, simultaneous application of high-frequency vibration (frequency 50-100 Hz, amplitude 0.05-0.1 mm), and step-by-step pressure increase to 5-8 MPa; Stage 2: Reduce microwave power by 30%, increase temperature by 1-2°C / min to 180-200°C, apply low-frequency vibration (frequency 20-50 Hz, amplitude 0.1-0.3 mm), and hold pressure for 60-90 min. S5: Gradient cooling and demoulding: After curing, the temperature is gradually lowered to below 50°C at a rate of ≤5°C / min. After demoulding, the surface of the warp knitting machine needle core bed is laser-finished. The dimensional tolerance is controlled at ±0.05mm and the surface roughness Ra≤0.4μm.

2. The process for preparing a high-pressure compression-molded carbon fiber composite warp knitting machine needle core bed according to claim 1, characterized in that: The prepreg resin matrix in S1 is added with a nano-silicon dioxide modifier in an amount of 0.5-1.0 wt %. After modification, the elongation at break of the resin matrix is ​​≥5%, and the interface shear strength is ≥45 MPa.

3. The process for preparing a high-pressure compression-molded carbon fiber composite warp knitting machine needle core bed according to claim 1, characterized in that: In the S4, high-frequency vibration and low-frequency vibration are applied in different areas, wherein high-frequency vibration is applied preferentially to the needle core bed slot area of ​​the warp knitting machine, and low-frequency vibration is applied to the plane area, and the vibration acceleration gradient is 5-20g.

4. The process for preparing a high-pressure compression-molded carbon fiber composite warp knitting machine needle core bed according to claim 1, characterized in that: The thickness of the microwave sensitization layer is 50-100 μm, and the microwave absorption efficiency is increased by 40-60% compared with the uncoated mold. The mold is internally integrated with a conformal cooling channel with a diameter of 3-5 mm. The cooling medium is thermal oil, and the temperature control accuracy is ±3°C.

5. The process for preparing a high-pressure compression-molded carbon fiber composite warp knitting machine needle core bed according to claim 1, characterized in that: The pressure control in step S4 adopts a dynamic feedback mechanism to adjust the pressure curve in real time according to the resin flow index. The matching relationship between the resin flow front speed and the vibration frequency is: When the resin flow rate is ≤0.1mm / s, the vibration frequency is ≤30Hz; When the resin flow rate is greater than 0.1 mm / s, the vibration frequency increases to 50-100 Hz.

6. The process for preparing a high-pressure compression-molded carbon fiber composite warp knitting machine needle core bed according to claim 1, characterized in that: The segmented structural design of the warp knitting machine needle core bed is divided into 10-15 segments along the length direction. The segments are connected by Z-shaped step surfaces with an angle of 25-35° and a gap of 0.1-0.3mm between the segments. The segments are connected by epoxy film (thickness 0.1-0.2mm) and titanium alloy screws.