The characteristics of vacuum-assisted forming of composite materials

2022-08-19 10:04

Vacuum Assisted Resin Infusion (VARI), namely Vacuum Infusion Process (VIP) or Vacuum Assisted Resin Transfer Molding (VARTM), is a new and low-cost molding technology for producing large composite parts. It is a process method that removes the gas in the fiber reinforcement in a vacuum state, uses the flow and penetration of the resin to impregnate the fiber and its fabric, and cures it at a certain temperature to form a certain resin/fiber ratio. The figure shows a schematic diagram of the vacuum-assisted forming process.

As a high-performance, low-cost, non-autoclave forming technology, VARI forming technology is gaining more and more attention in the aerospace field and is planned by CAI as a key low-cost manufacturing technology. VARI molding technology is a molding method that uses the flow and penetration of resin to impregnate fibers and their fabrics under vacuum pressure, and solidify them under vacuum pressure. Compared with the traditional process, the VARI molding technology does not require an autoclave, but only requires a single-sided rigid mold (the upper mold of which is a flexible vacuum bag film) for laying fiber reinforcements. The mold is only to ensure the structural type. Meet the surface requirements, simplify the mold manufacturing process, save costs, and only form under vacuum pressure without additional pressure, which helps to reduce costs. Therefore, its main features are low cost, low product porosity, performance close to the autoclave process, and suitable for manufacturing large-scale parts. The VARI method aims at the limitations of the RTM method, and through appropriate process measures, the curing process of the structure is only completed under vacuum conditions. The method is free from reliance on autoclave facilities and is a manufacturing method with clear low-cost potential for large structures. But like other resin transfer methods, this method has higher requirements on the fluidity of the resin. At the same time, in terms of realizing high-performance materials, the difficulties encountered in the low-pressure molding process will be greater than those in the high-pressure molding process. Therefore, the expectations for the mechanical properties of the material cannot simply be compared with the prepreg process method. The design concept for the structure requires a corresponding update. The engineering development of the VARI method urgently requires the synergy of materials, processes and designers. The VARI process mainly has the following characteristics:

① Derived from RTM process, the basic features are the same as RTM;

② Unlike RTM, resin flow is driven by vacuum pressure;

③ One side of the mold, the other side is a vacuum bag, only one side of the product is smooth;

④ The mold usually needs to be heated to meet the resin curing conditions;

⑤ The degree of mechanization and automation is low, and the production cycle is long;

⑥ Low production cost.

Although VARI has many advantages, as a liquid molding technology, there are still many difficulties to be solved in the process of composite material molding, such as the control of resin flow, the prevention of dry spot and the consistency of resin/fiber ratio. In-depth research on micro and macro mechanisms.

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