VARTM preform system

Occasionally, fibers or tows are inserted or laid into a shape as a preform, and the whole preform is subjected to the injection of the resin system under pressure, such as resin transfer molding (RTM) vacuum-assisted resin transfer molding (VaRTM) or even partial injection of the resin or part of the resin system, with the same qualified resin transfer molding (SqRTM) process. In every case, there is the real possibility of fibers moving under the influence of the injected resin, producing considerable doubt as to the final formal structure, position, or integrity of the fibers after molding. 

Due to the flexible vacuum bagging system used in VARTM, a composite part manufactured by VARTM could have a thickness non-uniformity issue. Generally, better thickness control (i.e., preform compaction relaxation) can be achieved during the post-mold filling process if one allows enough time for the excess resin to be completely vented out from the resin saturated fiber preform with all resin inflow gates closed. Under such a scenario, the whole fiber preform could be uniformly compacted to its compaction limit (or fiber volume fraction limit) under the pressure difference between the environmental pressure and the vacuum pressure. The preform compaction relaxation can either be measured from experiments or predicted by numerical simulation tools. 

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