Research On The On-line Sensing And Monitoring System In Liquid Composites Molding

Advanced composites are a new type of important materials. However, their applications are limited due to the high cost. How to develop new manufacturing techniques and reduce the manufacturing cost of high-quality composites are the urgent technology questions to solve. Liquid Composite Molding (LCM) process has been representing the promising development direction of composites manufacturing techniques with high quality and low cost for its outstanding operation for large structure or function parts with complex geometry in one step. With the aid of National 863 Plan (2001AA335020), according to the development demands of high quality and low cost LCM integration manufacturing technology, the on-line sensing and monitoring in the molding process of LCM was investigated systemically.In this paper, the study status in LCM abroad and at dome was commented on generally and the molding process was numerical simulated. Then the micro-flow in the single fiber bundle and the effects of primary parameters, test methods and the common fiber draping defect on the preform permeability were studied. Meanwhile, the multifunctional integrative on-line sensing including flow-front and curing in LCM was realized by using the long-short period fiber grating and an optimal sensor placement method solved by SGA was proposed. Finally, based on these researches, a primary prototype system of on-line sensing and monitoring in LCM was established. The followings were achieved.(1) According to the quantitative characterization of pressure field, velocity field, temperature field and cure degree, the numerical methods to predict the resin flow front spread and curing process were presented. The 2D and 3D numerical analysis in the mold filling process and curing of LCM were carried out using the three-angle element and six-node wedgy element control volume / finite method. Furthermore, it was validated by the examples and experiments.(2) The micro-flow in the single fiber bundle and its simulation were studied. Then the effects of primary parameters (including fiber structure, fiber volume content, temperature, capillary pressure and injection pressure / velocity), test methods andthe common fiber draping defect (namely race tracking) on the preform permeability and its numerical simulation were investigated, which provided the necessary theoretical and technology bases for the accurate permeability prediction, enhancing the LCM simulation emulation precision, reducing and avoiding the defects formation and optimizing process parameters.(3) The sensing measurements of the flow front and the intercross sensitive parameters of temperature / viscosity and stress in curing were solved using the long-short period fiber grating. And the key change process such as gel, cure end and temperature drop could be observed directly. It realizes the multifunctional integrative on-line sensing of flow front and cure process, which pioneers a new approach for the intercross sensitive sensing of fiber gratings in composites.(4) A sensor property evaluation method together with the practical process conditions was proposed to obtain the maximum flow information with the least sensors. The mold filling pattern in the closed mold cavity could be identified to detect the nonideal flow cases according to the response of limited sensors. Furthermore, the sensor placement was optimized by the method of SAG, which consumedly enhanced the calculation efficiency.(5) Based on the above researches, a primary prototype of on-line sensing and monitoring in LCM was established. It contained three modules including the LCM numerical simulation emulation, the optimal sensor placement and the graphic user interface LOSP of LCM on-line sensing. Through the validation of LCM experiments, the LOSP platform could automatically judge and identify different mold filling patterns, and dynamically make decisions of corresponding strategic measurements according to the collected resin flow front information, which eliminated defects such as dry spots. The curing process was also monitored to adjust the process, which realized the LCM on-line quality sensing. This research supplied theoretical directions and established the technology base for the realization of LCM automatic production.