The main principle of the RTM process is to place reinforcement preforms designed according to performance and structural requirements in the mold cavity, using injection equipment to inject a special resin system into the closed mold cavity, the mold has peripheral sealing and fastening, and injection and exhaust systems , in order to ensure smooth flow of resin and discharge all the gas in the cavity and thoroughly infiltrate the fibers, it also has a heating system, a pressure holding system, and a forming process that can be heated and solidified to form composite components. It is a forming method that does not use prepreg or autoclave. Therefore, it has the advantages of high efficiency, investment, and greenness, and is a manufacturing technology with potential for the development of the new generation of aircraft airframes in the future.
Resin transfer molding technology is a low-cost composite manufacturing method. Originally mainly used for aircraft secondary load-bearing structures, such as doors and inspection hatches. In 1996, the US Defense Research Agency carried out research on low-cost RTM manufacturing technology of high-strength main bearing components. At present, the manufacture of small and medium-sized composite RTM parts has been widely used, and large-scale RTM parts have also been successfully applied on the vertical tail of JSF. Resin transfer molding is a low-cost composite manufacturing method that was 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. At present, the manufacture of small and medium-sized composite RTM parts has been widely used, and large-scale RTM parts have also been successfully applied on the vertical tail of JSF. The advantages of this method are that it is environmentally friendly, the formed laminate has good performance and good double-sided quality, and its application in aviation can not only reduce its own labor, but also reduce assembly workload due to the ability to form large integral parts. However, the parts formed by pressure injection of resin into the mold cavity have defects such as large pore content, low fiber content, uneven distribution of resin in fibers, and insufficient resin impregnation of fibers, so this technology has potential for improvement.
The equipment used for the RTM process is called "RTM integrated forming equipment". In fact, this is not only a piece of equipment, it should be a set of equipment to be precise, including: reaction kettle, vacuum equipment, injection exhaust system, heating system, pressure maintaining System, mold and other equipment, this system is to organically integrate the above equipment according to the RTM process.
At present, in addition to foreign production of such equipment, only Bairuo Instruments in China has the ability to produce RTM integrated forming equipment with a pressure holding capacity of 200 tons, breaking the situation that imported equipment dominates the world. The equipment integrates the functions of the upper and lower molds to move, turn over, mold clamping, mold clamping overturning, mold heating, pressure holding, injection, etc. It meets the requirements of RTM production automation in composite material production enterprises.
At present, the main production of RTM equipment: aircraft door, tail, propeller, etc.
The advantages of using the RTM process are:
Both the intervening molded body and the resin material used in the resin transfer molding process are less expensive than prepregs, can be stored at room temperature, and have less volatile components and less environmental pollution during the molding process. Using this process, thicker net-shaped parts can be produced while eliminating many post-processing steps.
The process also helps to produce complex parts with precise dimensions and superb surface finishes.
Another feature of the resin transfer molding process is that it allows core filler material to be placed in the preform before closing the mold, preventing the preform from being squeezed during mold closing. The proportion of the core mold in the whole preform is low, about 0-2%.
This process can produce heterosexual bodies with high strength, low density and small deformation.
In short, resin transfer molding (RTM) can be used as an efficient and repeatable automated manufacturing process to greatly reduce processing and molding time, reducing the traditional hand lay-up process from days to hours or even tens of minutes.
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