Study On Resin Flow Behavior In Vacuum Infusion Molding Process

Vacuum infusion molding process (VIMP) is a recently developed, cost-effective liquid composite molding (LCM) technique used to manufacture large scale composite structures. Fiber preform is placed on a tool surface and covered by a flexible bag film. The cavity is sealed by vacuum tapes. A vacuum is drawn on the system to infuse the reactive resin to wet out the fiber preform. In the vacuum infusion molding process, complete filling of the mold with adequate wetting of the fibrous perform is critical to the product quality. To solve this problem, adequately understanding the resin flow behavior in the vacuum infusion molding process is critical to predict the successive resin flow front and the pressure distribution for process control and parameter optimization. Based on the study of the resin flow behavior in the vacuum infusion molding process, some critical issues of VIMP have been studied. The chemorheology of two different resin systems for VIMP was investigated and their low viscosity processing windows were well determined. Permeability test method and the effects on the preform permeability were systematically investigated. The influences of major processing and material parameters in VIMP have been systematically studied. Finally, the processing properties of VIMP and the design of resin/vacuum road in VIMP were illustrated.The rheological behavior of two resin systems for vacuum infusion molding process (VIMP) was studied with DSC and viscosity experiments. The rheological model of the resin was established based on Dual-Arrhenius equation and chemical reactive equation. The model was used to simulate rheological behaviors of the resin. The estimated viscosity values of the resins were in good agreement with that of the experiments. The low viscosity processing window of the resin for VIMP was determined based on the developed models. The developed viscosity models are important for processing simulation and quality control for vacuum infusion molding processing of high performance composites.Effects of injection pressure, viscosity, porosity, configuration of fabric, kind of liquid and fiber on the permeability of fiber preform have been studied. The result has been used as reference to calculate the molding filling time. According to the compressed characteristic of the preform under vacuum, vacuum-plastic-bag-test method has been applied to test the permeability of distribution medium and reinforcement perform of VIMP. The average permeability of distribution medium is 1.30×10^-8m², that is 10～100 times as the average permeability of fiberglass preforms. The apparent permeability values were increased by 10 times, 6 times and 4 times respectively when distribution medium was incorporated into 10 layers, 20 layers, 30 layers of 4:1 fabric performs, respectively, as a surface layer. In the vacuum infusion molding process, due to the existence of two distinct flow medium, the fiber preform and the distribution medium, the resin flow behavior is more complicated than that in the resin transfer molding (RTM) process. As a surface layer or a middle layer, the existence of distribution medium can speed up the velocity of resin flow and reduce the molding filling time. Difference of distance between the resin flow front position on preform surface and that on undersurface linearly were increased with the thickness of fiber preform.The effects of peel ply, gravity, infusion methods, ways of pumping air on the resin flow behavior in vacuum infusion molding process has been studied. The results show that the existence of peel ply can slightly speed the velocity of resin flow; both the flow modes and molding filling velocity of the resin change with resin infusion methods and ways of pumping air; the resin molding filling velocity increases with the diameter of infusion pipe; the influence of gravity on the resin flow rate increases with obliquity of the resin flow direction.In the vacuum infusion molding process based on grooves, the number and dimension of grooves has a significant effect on the resin molding filling velocity, molding filling time and the quality of fiber wetting. The molding filling time decreases with the reduction of space between grooves when the width of grooves was fixed.Finally, based on the estimated low viscosity processing window of the resin, the evaluated molding filling time and the resin behavior in vacuum infusion molding process, the resin/vacuum tunnel design in vacuum infusion molding process was investigated systematically. The design results have been applied to guide the integrally manufacturing process of large scale composite turbine blades. According to the integrally manufacturing process, the processing properties of VIMP and the cause of defect formation were analyzed, which provides a useful reference for VIMP design and modification.