Carbon fiber composite materials need to be processed by molding processes from prepreg to final parts. With the development of carbon fiber technology, the molding process of carbon fiber composite materials is also constantly improving. However, the various molding processes of carbon fiber composite materials do not exist in a way of updating and elimination. Often, multiple processes coexist to achieve the best effects under different conditions and circumstances. The following lists the 12 most commonly used carbon fiber composite molding processes at this stage. Let's see which ones you know.
Spray molding process
It belongs to a type of low-pressure molding in hand lay-up process. After the short-cut fiber and resin are mixed by a spray gun, compressed air is sprayed on the mold. After reaching the predetermined thickness, it is manually pressed with a rubber roller and then cured. 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 transition layers for automobile bodies, hulls, bathtubs, and storage tanks.
Winding molding
The continuous fiber or cloth tape impregnated with resin glue is wound onto the core mold according to a certain pattern, and then cured and demolded to become a composite product. Carbon fiber winding molding can give full play to its high specific strength, high specific modulus and low density. The product structure is simple and can be used to manufacture cylinders, spheres and some positive curvature rotation bodies or cylindrical carbon fiber products.
Liquid molding
The process of synthesizing liquid monomers into high molecular polymers and then curing the polymers into composite materials is changed to be completed directly in the mold at the same time, which not only reduces the energy consumption in the process, but also shortens the molding cycle (it only takes about 2 minutes to complete a product). However, the application of this process must be based on precise pipeline transportation and metering as well as automatic temperature and pressure control. It belongs to the intersection of polymer materials and modern high-tech science and technology, and its current application is not very wide.
Liquid molding mainly includes: RTM molding process, RFI molding, and VARI molding.
The main advantage of the resin film infiltration (RFI) molding process is that the mold is simpler than the RTM process mold, the resin flows along the thickness direction, it is easier to infiltrate the fiber, there is no prepreg, and the cost is lower. However, the dimensional accuracy and surface quality of the resulting product are not as good as the RTM process, the void content is higher, and the efficiency is slightly lower. It is suitable for the production of large flat or simple curved parts.
The advantages of the vacuum assisted molding process (VARI) are high raw material utilization, less finishing and processing of parts, no need for prepreg, low cost, and suitable for the production of large wall 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: Resin Transfer Molding) technology is a low-cost composite material manufacturing method, which was originally mainly used for aircraft secondary load-bearing structural parts, such as doors and inspection covers. In 1996, the US Defense Advanced Research Projects Agency conducted research on low-cost RTM manufacturing technology for high-strength main load-bearing components. RTM technology has the advantages of high efficiency, low cost, good part quality, high dimensional accuracy, and little environmental impact. It can be used for the molding of large, complex, and high-strength composite parts. It has become one of the most active research directions in the field of aerospace material processing in recent years.
Compression molding
Place the carbon fiber prepreg between the upper and lower molds, close the mold and place the mold on the hydraulic molding table. After a certain period of high temperature and high pressure to solidify the resin, remove the carbon fiber product. This molding technology has the advantages of high efficiency, good product quality, high dimensional accuracy, and little environmental impact. It is suitable for batch molding of high-strength composite parts. However, the initial mold manufacturing is complex, the investment is high, and the size of the part is limited by the size of the press.
Injection molding
This is a new technology. Bole CIML equipment integrates the traditional "multi-step method" process into a "one-step method", which greatly shortens the process flow and better retains the fiber length, achieving the purpose of energy-saving and efficient production. By overcoming a series of key technical issues such as formula optimization, mixing system, intelligent control system and molding process parameter optimization in materials-equipment-manufacturing, it fully meets the requirements of automobile lightweighting for product strength, cost, efficiency, etc., and can be called a tailor-made equipment tool for automobile lightweighting.
Hand lay-up molding-wet layer molding method
Apply 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, mold, cure and demold. Today, with the highly developed preparation technology, the hand lay-up process is still widely used in many fields such as petrochemical containers, storage tanks, and automobile shells due to its advantages of simple process, low investment, and wide application. Its disadvantages are loose texture, low density, low product strength, and it mainly relies on manual labor, unstable quality, and low production efficiency.
Vacuum autoclave
Put the composite material blanks made by stacking single-layer prepreg in a predetermined direction in the autoclave and complete the curing process at a certain temperature and pressure. The autoclave is a special pressure vessel that can withstand and regulate a certain temperature and pressure range. The blanks are laid on the surface of the mold with a release agent, and then covered with porous anti-sticking cloth (film), adhesive felt, and breathable felt in turn, and sealed in a vacuum bag, and then placed in the autoclave. Before heating and curing, the bag is first evacuated to remove air and volatiles, and then heated, pressurized, and cured according to the curing system of different resins. The formulation and implementation of the curing system are the key to ensuring the quality of autoclave molded parts.
Suzhou Norn Composite Materials used the autoclave molding process when customizing military transport boxes for a military enterprise. The military transport box products produced have a smooth appearance and stable structure, and finally passed the military's acceptance review. The vacuum autoclave molding process has many advantages. It can not only solidify laminates of different thicknesses and manufacture parts with complex curved surfaces, but also has very reliable mechanical properties. However, the corresponding vacuum autoclave molding also has some disadvantages, such as the size of the parts is limited by the size of the autoclave, and the energy consumption is high, resulting in relatively high operating costs.
Vacuum introduction
Abbreviated as VIP, lay "dry" carbon fiber composite materials on the mold, then lay vacuum bags, and extract the vacuum in the system to form a negative pressure in the mold cavity. The pressure generated by the vacuum is used to press the unsaturated resin into the fiber layer through the pre-laid pipeline, so that the resin can infiltrate the reinforcing material and finally fill the entire mold. After the product is cured, the vacuum bag material is removed to obtain the desired product from the mold.
In a vacuum environment, the resin impregnates the carbon fiber, and very few bubbles are generated in the product. The product has higher strength and lighter weight, and the product quality is relatively stable. In addition, the loss of resin is reduced. Only one side of the mold can be used to obtain a product with smooth and flat surfaces on both sides, and the thickness of the product can be better controlled. It is generally used in rudders and radar shields in the boat industry, blades and engine covers in wind power energy, and various roofs, windshields, and compartments in the automotive industry.
3iTech Induction Heating
A new induction heating process that integrates sensors in the mold can process carbon fiber at temperatures of 20℃-400℃, and heat the mold surface by using sensors integrated inside the mold through heat conduction. This is a supplementary technology launched by the emerging company RocTool on the Cage system. Electromagnetic induction can quickly heat the mold and can well control the local temperature. Its advantage is that it significantly reduces cycle time and component costs. However, this technology is not suitable for large components at present, and the related output must be large enough.
Lamination molding
Place the prepregs stacked layer by layer between the upper and lower flat molds for pressurization and heating for 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 materials of various specifications and different uses. It has the characteristics of high mechanization and automation, stable product quality, etc., but the one-time investment in equipment is large.
Pultrusion molding
Under the action of traction, continuous carbon fiber tows, belts or cloth impregnated with resin glue are formed and cured through an extrusion die to continuously produce profiles of unlimited length. Pultrusion molding is a special process in the composite molding process. Its advantage is that the production process can be fully automated and the production efficiency is high.
The fiber mass fraction in pultruded products can be as high as 80%. The impregnation 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 requirements of the product. This process is suitable for producing profiles of various cross-sectional shapes, such as I-shaped, angled, grooved, special-shaped cross-sectional pipes and combined cross-sectional profiles composed of the above cross-sectional shapes.
Since its establishment, Suzhou Noen Composite Materials has been focusing on the field of carbon fiber. It is not only equipped with complete carbon fiber core production equipment, such as carbon fiber hot pressing molding machines, autoclave curing furnaces, etc., but also has established a dedicated laboratory to analyze and develop innovative functional materials. In the carbon fiber industry, it has always adhered to the principle of customer first and provided customers with more high-quality carbon fiber products.