Carbon fiber composite materials need to be processed using a molding process from prepreg to the final part. With the development of carbon fiber technology, the molding process of carbon fiber composite materials is also constantly improving. However, various molding processes of carbon fiber composite materials do not exist in the way of updating and eliminating, and often a variety of processes coexist to achieve the best effect under different conditions and different situations.
What is the Carbon Fiber Forming Process?
- Injection molding process:
It belongs to a type of low-pressure molding in the hand lay-up process. After mixing chopped fiber and resin with a spray gun, compressed air is sprayed on the mold, and after reaching a predetermined thickness, it is manually pressed with a rubber roller, and then cured and formed. A semi-mechanized molding process created to improve hand lay-up molding has a certain degree of improvement in work efficiency, but it still cannot meet mass production. It is used to manufacture the transition layer of automobile bodies, hulls, bathtubs, and storage tanks.
- Winding molding:
The process of winding continuous fibers or cloth tapes impregnated with resin glue on a core mold according to a certain rule, and then curing and demolding into composite products. Carbon fiber winding molding can give full play to its characteristics of high specific strength, high specific modulus, and low density.
- Liquid molding:
The liquid monomer is synthesized into a high molecular polymer, and then the process of curing the polymer into a composite material is changed to be completed directly in the mold at one time, which not only reduces the energy consumption in the process but also shortens the molding cycle. However, the application of this process must be based on precise pipeline transportation and metering, as well as automatic temperature and pressure control. Liquid molding mainly includes the RTM molding process, RFI molding, and VARI molding. The main advantages of the resin film infiltration (RFI) molding process are that the mold is simpler than the RTM process mold. The resin flows along the thickness direction, it is easier to infiltrate the fibers, there is no prepreg, and the cost is lower. However, the dimensional accuracy and surface quality of the obtained products are not as good as those of the RTM process, the void content is higher, and the efficiency is slightly lower, which is suitable to produce parts with large planes or simple curved surfaces. The advantages of the vacuum-assisted forming process (VARI) are a high utilization rate of raw materials, less trimming and processing, no need for prepregs, and low cost. It is suitable to produce large-scale panel structural parts at room temperature or low temperature. But the disadvantages are similar to the RFI molding process.
- Resin Transfer Molding (RTM):
Resin Transfer Molding (RTM) technology is a low-cost method of manufacturing composite materials that were initially primarily used for aircraft secondary load-bearing structures such as doors and inspection hatches. In 1996, the US Defense Advance Research Agency carried out research on low-cost RTM manufacturing technology of high-strength main bearing components. RTM technology has the advantages of high efficiency, low cost, good quality of parts, high dimensional accuracy, and little impact on the environment. It can be applied to the molding of composite parts with large volumes, complex structures, and high strength. One of the most active research directions in the field of material processing.
- Compression molding:
The carbon fiber prepreg is placed between the upper and lower molds, and the mold is placed on the hydroforming table. After a certain period of high temperature and high pressure to solidify the resin, the carbon fiber product is removed. This molding technology has the advantages of high efficiency, good product quality, high dimensional accuracy, and less environmental impact, and is suitable for the molding of mass and high-strength composite parts. Mold manufacturing is complex, the investment is high, and the size of the parts is limited by the size of the press.
- Injection molding:
This is a new technology, bole CIML equipment integrates the traditional multi-step process into a one-step process, which shortens the process flow. The fiber length is better preserved to achieve the purpose of energy-saving and high-efficiency production. By overcoming a series of key technical problems such as formula optimization, compounding system, intelligent control system, and molding process parameter optimization in material-equipment-manufacturing, it fully meets the requirements of vehicle light weighting in terms of product strength, cost, and efficiency. A weapon tailored for lightweight automobiles.
- Hand lay-up--wet lay-up method:
Apply mold release agent and gel coat on the working surface of the mold, lay the cut carbon fiber prepreg on the working surface of the mold, brush or spray the resin system glue, and after reaching the required thickness, form, solidify, and demold. With highly developed preparation technology, the hand lay-up process is still simple in process and low in investment. The advantages of wide application and other advantages are widely used in many fields such as petrochemical containers, storage tanks, and automobile shells. The disadvantage is that the texture is loose, the density is low, the product strength is not high, and it mainly depends on labor, the quality is unstable, and the production efficiency is low.
- Vacuum autoclave:
The composite material blank formed by laying up a single layer of prepreg material in a predetermined direction is placed in an autoclave, and the curing process is completed under a certain temperature and pressure. An autoclave is a special pressure vessel that can withstand and regulate a certain temperature and pressure range. The blank is laid on the surface of the mold with a release agent, then covered with porous release cloth (film), absorbent felt, and the air felt in sequence, sealed in a vacuum bag, and then placed in an autoclave. Before heating and curing, vacuum the bag to remove air and volatiles, and then heat up, pressurize and cure according to the curing system of different resins. The formulation and implementation of the curing system are the keys to ensuring the quality of autoclaved parts.
- Vacuum import (VIP):
Lay carbon fiber composite material on the mold, then lay a vacuum bag, and draw out the vacuum in the system to form a negative pressure in the mold cavity. And use the pressure generated by the vacuum to press the unsaturated resin into the fiber layer through the pre-laid pipeline, let the resin infiltrate the reinforcing material, and finally fill the entire mold. After the product is cured, remove the vacuum bag material, and obtain the desired product from the mold. When resin infiltrates carbon fiber in a vacuum environment, there are very few bubbles generated in the product. The product has higher strength, lighter weight, stable product quality, and reduces the loss of resin, and only one side of the mold can be used to obtain smooth and flat products on both sides. Can better control product thickness. In rudders and radar shields in the marine industry, blades and cabin covers in wind power energy, and various types of roofs, windshields, and carriages in the automotive industry.
- 3iTech induction heating:
A new type of induction heating process that integrates an inductor into the mold. Which can process carbon fibers at a temperature of 20°C-400°C, and heats the surface of the mold with an inductor integrated inside the mold through heat conduction. The use of electromagnetic induction can rapidly heat the mold and can control the local temperature well. The advantage is a significant reduction in cycle time and component cost. The technology is currently not suitable for large components, and the relevant production volume must be large enough.
- Lamination molding:
The layer-by-layer prepreg is placed between the upper and lower flat molds for pressure heating and curing. This process can directly inherit the production methods and equipment of wood plywood, and improve and perfect it according to the rheological properties of the resin. The lamination molding process is mainly used to produce composite sheets of various specifications and uses. It has the characteristics of a high degree of mechanization and automation, and stable product quality, but the one-time investment in equipment is large.
- Pultrusion:
Under the action of traction, the continuous carbon fiber tow, belt, or cloth impregnated with resin glue is formed and cured by extrusion die to continuously produce profiles of unlimited length. Pultrusion is a special process in the composite material forming process. Its advantages are that the production process can be fully automated and controlled, and the production efficiency is high. The fiber mass fraction in pultruded products can be as high as 80%. The dipping is carried out under tension, which can give full play to the role of reinforcing materials. The product has high strength. The longitudinal and transverse strength of the finished product can be adjusted arbitrarily, which can meet the different mechanical properties of the product. Require. This process is suitable for producing profiles with various cross-sectional shapes, such as I-shaped, angle-shaped, groove-shaped, and special-shaped section pipes, and combined section profiles composed of the above-mentioned sections.
The Difference Between Dry Forming and Wet Forming of Carbon Fiber
In the production field of carbon fiber products, there are dry carbon fibers and wet carbon fibers. The distinction is expressed in the production process of carbon fiber products. The two most used methods for processing carbon fiber composites are prepreg autoclave forming mode and vacuum introduction mode.
There are obvious differences in the performance of the products produced by the two processes. The wet process is prone to deformation during processing and the truncation part is prone to de-filamentation. The resin and fiber have poor bonding properties and are prone to oxidative discoloration due to contact with air. The dry prepreg process does not have the above situation, but it is prone to performance degradation under UV irradiation. The carbon fiber products produced by these two production methods are significantly different in weight and hardness. Carbon fiber products refer to the use of carbon fiber prepregs as raw materials, which are processed into material products that can meet the requirements of users through different processing methods.
Carbon fiber parts are lighter than metal aluminum, but stronger than steel, and have the characteristics of corrosion resistance and high modulus. They are important materials in national defense, military industry, and civilian use. It not only has the inherent intrinsic properties of carbon materials but also has the soft processability of textile fibers. It is a new generation of reinforcing fibers. Compared with dry carbon fiber, the carbon fiber pattern of wet carbon fiber will be deformed when vacuuming, and carbon fiber filaments will also be seen in its cross-section, while dry carbon fiber products will not.
The carbon fiber products made by the dry process have good hardness and are easy to be processed by CNC, but the production cycle is long and it is not easy to mass-produce, and the production cost is high. Carbon fiber products refer to the use of carbon fiber prepregs as raw materials, which are processed into material products that can meet the requirements of users through different processing methods. The cost of wet molding products is low, the production process is relatively simple, and the production efficiency of the process is high. In the current production of carbon fiber, dry forming is used in the case of high precision and high-quality requirements, and wet forming is used in appearance parts and mass production.
