Composite materials are made of two or more materials with different properties, and they are macroscopically composed of materials with new properties through physical or chemical methods. Compared with conventional composite materials such as reinforced concrete, the new lightweight, high-strength composite materials with carbon fibers and glass fibers as reinforcing materials have been developed in the past 50 years and are also known as advanced composite materials.
Composite hull VARI process forming
After decades of development, advanced composite materials have been widely used in the aerospace field due to their superior properties such as high specific modulus, high specific strength, and high corrosion resistance. In the aerospace field, due to the obvious effect of light weight composite materials in terms of weight loss increase range, and superior performance in heat prevention enhancement, more and more components adopt composite materials from nose cones, throat linings to missile bodies and engine casings. To produce. Also in aerospace manufacturing, in the past few decades, composite materials have gone through a period from being used only for non-supporting components such as fairings, to sub-supporting locations for empennage, and finally successfully applied to military aircraft and civil aircraft. The development process of the main bearing structure makes composite materials no longer play a role of weight reduction alone, and its enhanced performance and reliability have also been recognized.
In spite of this, after several decades of process improvement, the cost of manufacturing composite materials and the cost reduction of raw materials are still lower than people's expectations. At present, the raw material cost of carbon fiber reinforced epoxy prepreg is still 5 to 10 times higher than that of aluminum alloy, and the manufacturing cost is higher. Although the co-curing technology can reduce costs by achieving a high degree of integration of components and reducing the number of parts, it has been proved that it brings higher cycle costs and non-cyclical costs. On the other hand, the traditional prepreg/autoclave molding process is not tried on any component. Although some components with complicated shapes or high load-bearing loads have been attempted to be produced using this process, they are often replaced by metallic materials because of excessive costs. It can be seen that the high cost reduces the market competitiveness of composite components to a great extent and limits the further promotion of the composite structure.
Sine wave beam RTM injection simulation
It can be seen that to further increase the amount of composite materials used in the aerospace industry, it is necessary to seek a low-cost molding process, and the resin transfer molding (RTM) process is one of the most promising processes for reducing the structural cost of composite materials. This process uses a low-viscosity resin to inject the closed mold. The resin flows along the gaps between the pre-layed or pre-formed reinforcing materials and infiltrates the reinforcing material. After the injection molding is completed, the mold is heated and cured by the mold. Compared with other traditional composite molding processes, RTM has many advantages: it is suitable for producing complex shaped composite components, it can obtain smooth double surfaces without gel coat resin, and has short production time from design to production, high production efficiency, and production equipment. Simple and so on. RTM molds and products can be designed using CAD, mold making is relatively easy, and material selection is extensive. RTM molded parts are easy to achieve local reinforcement and local thickening. Complex components (such as skin-reinforced structures) that require previous bonding are easy to form once. The resin volatilization during the molding process of the RTM process is beneficial to labor protection and environmental protection. In terms of cost, compared to the prepreg molding process, the price per unit mass of the RTM process can be reduced by 30% to 50%. With the continuous improvement of the process level, the RTM process also achieved the formation of the main bearing structure of the aircraft. The application of RTM technology has injected new vitality for the further promotion of composite materials in the aerospace industry.
RTM process and mold design
The production process of the composite RTM molding process consists of the following five steps:
(1) Preform: The dry material of the reinforcement body is processed into the shape required by the part, and then put into the cavity, leaving no gap between the reinforcement body and the inner wall of the cavity as far as possible;
(2) Injection molding: The resin is injected into the cavity through the injection device, and the resin flows between the gaps of the reinforcement body and infiltrates the reinforcement body;
(3) Curing: After the resin fully fills the cavity, the resin in the cavity is heated by the heating device on the mold to make it fully solidified;
(4) Open mold: separate the upper and lower molds of the cavity, remove the cured composite material components, such as removable core and disassemble core;
(5) Trimming: Trim the composite material, cut off the edge reserved for the entry and exit glue holes, and do a proper grinding to ensure smoothness.
Hull VARI Injection Molding (PPE)
The processing equipment involved in the RTM process mainly includes the injection device and the mold. The uses of the mold include reinforcement body preforming, determining the component topography and resin flow path, heat curing of the resin, and ensuring mold release. According to the different components to be produced and the different process solutions, the mold has extremely high designability. According to the characteristics of the integrated design of the composite structure and process, designing the mold at the same time as the part design is very necessary.
In the injection molding process of large-scale structural parts, if the choice of the plastic injection and the rubber dispensing system is not appropriate, the pouring time will be too long, and the resin will partially solidify before the component is completely filled, resulting in deterioration of the resin flowability, and eventually causing the components to deteriorate. Can not be fully formed into waste; improper choice of plastic injection system and the plastic system will result in increased resin consumption, waste of resin, or even need to modify or design tooling / mold, resulting in increased process costs. In addition, the correct choice of plastic injection and dispensing system can also reduce the number of dry spots in the molding process of composite structural parts and avoid bubble generation. For complicated structural parts, the positions and quantities of the rubber injection ports and the rubber discharge ports should be reasonably arranged, and the rubber injection ports and the rubber discharge ports should be opened and closed in a timely manner. Problems in the process can also be avoided, and modification or redesign of tooling can be avoided. / Mold, improve product quality.
The RTM process technology requires the design and processing of suitable tooling equipment prior to production to determine the appropriate process parameters. How to design a tooling/die that satisfies both the production process requirements and the product quality requirements at a lower cost and cycle has always been one of the hot topics actively explored in the industry. The traditional method is to try out molds based on experience, which not only takes time and labor, but also makes it difficult to ensure product quality. It has been difficult to meet the needs of modern composite tooling/die design and production. The use of digital technology for simulation during the process design and manufacturing process is one of the effective ways to increase development efficiency, reduce production costs, and improve product quality.
With the continuous development of CAE technology, reasonable digital simulation of design and production processes before tooling/mold design and product manufacturing, through the simulation results to guide the design and production, can avoid problems in the production and design process, rational design Tooling/mold is an important way to improve product quality and production efficiency.
PAM-RTM simulation aided mold design
ESI Group, Europe’s largest engineering software supplier, has been working on this research since more than a decade ago and has achieved impressive results. PAM-RTM as a professional RTM process simulation software is one of the important products in the composite material value chain of ESI Group. It can easily and accurately simulate the resin flow process, flow velocity, pressure distribution, curing process, and temperature in the RTM process. The results of distribution, optimization of mold design and process parameters, and reduction in design cycle time and cost have become RTM design and development tools widely used in the industry.
Fan blade VARI injection simulation
PAM-RTM is a cost-effective solution for analog liquid compound molding. Minimizing the risk of creating defective parts helps to master the tool design and manufacturing process. PAM-RTM provides a pre-designed, rapid solution and refines the process and mold optimization and final design verification calculations. Furthermore, PAM-RTM calculates time-to-market and reduces the cost of tool installation and injection processes.
The PAM-RTM simulation process covers a wide range of processes, including most RTM processes including closed-mold RTM, RTM considering mold heating, vacuum-assisted RTM (VARI), CRTM, and ACRTM; easy to operate, engineers can quickly Learn to operate; Calculate quickly, use DARCY's law to solve, ensure the accuracy of the calculation; intuitive post-processing results, no need to enter other interfaces to observe the simulation results; accurately simulate resin filling and curing process, optimize fiber and resin collocation, optimize injection The position of the mouth and the glue outlet optimizes the flow rate of the glue injection and the pressure of the glue injection. In summary, it can help companies significantly reduce design time costs and economic costs caused by a large number of trials, improve work efficiency, and improve corporate design capabilities.
The positions of the injection opening and the discharge opening are the earliest design parameters for RTM mold design work. Different positions of the rubber injection port and the glue outlet will directly affect the filling path of the resin, the total filling time, the pressure distribution of the resin in the cavity during the filling process, the forward flow speed of the resin, the amount of resin loss, and so on, thereby deciding whether the product is possible or not. There is a defect level such as the distribution and number of air bubbles and dry spots. Unreasonable injection/dispensing nozzle selection may even cause the resin to fail to fill up.
At the beginning of the mold design, computer simulation technology was used to simulate the filling process of the resin in the cavity in different injection/discharge port solutions. It can be predicted in advance whether the resin can fill the entire cavity, and the total injection time is reasonable, and The amount of resin loss, etc., thereby reducing the number of tryouts and avoiding the redesign of the mold as much as possible.
For a composite structural member with a complex structure, such as a one-time molding of a skin-reinforced structure, it is often required that a plurality of rubber injection ports and a plurality of outlet ports be controlled to achieve sufficient filling through corresponding switching process control. At this time, even if the same dispensing opening/dispensing opening distribution scheme is adopted, the filling/unloading conditions of the injection/delivery opening will be different. Therefore, the mold design must not only give the CAD number model of the mold, but also give the switching course scheme of each rubber mouth.
Using the PAM-RTM, you can control the opening and closing status of each rubber port by setting the control switches associated with the respective sensors. In order to simulate the injection molding of resin in various switching processes, a more reasonable resin injection program can be obtained quickly and efficiently.
Large-scale composite products such as ship hulls and wind turbine blades are often produced using a vacuum-assisted RTM molding process (VARI process). For these large-sized products, not only the position of the glue injection opening and the glue injection opening are required, but also the large member is often divided into a plurality of filling regions by using a diversion pipe, thereby avoiding the porous resin in the reinforcement. Long distances are transmitted in the medium, shortening the injection time and reducing the possibility of macroscopic dry spots.
Using computer simulation technology can quickly predict the impact of different diversion schemes on the injection molding process, and help mold designers quickly determine a more reasonable distribution of the diversion pipe.
Conclusion
With the characteristics of larger, thicker, more complex structures and higher integration requirements for composite products, RTM processes will receive more attention in various industrial fields. As the most significant equipment affecting product quality in RTM process-related equipment, RTM mold design is also facing a new round of challenges. The integration of computer simulation technology into the design of RTM molds can effectively improve design efficiency, avoid mold redesign as much as possible, and reduce the time and economic costs caused by multiple attempts.
Frp Grating,Gutter Grates,Sealed Gully Cover,Drain Gully Grates
Changxing Ro-spring Road Facilities Co., Ltd , https://www.enro-spring.com