Study On The Defects Formation Mechanism And Control Methods In Resin Transfer Molding

Resin transfer molding (RTM) is increasingly becoming a popular method for the manufacturing of composites parts especially with a low cost, environmental protection feature and large and complex geometries. This process has grown considerably in both area of application and research activities in recent years. However, defects always occur in the injection process of RTM, how to prevent voids, dry spot and perform deformation and minimize the mold filling time are the most important issues which need to study deeply. According to the new development of the RTM technique, the study of this paper includes two parts, one is the defects formation mechanism and effect factors, the other is the control method in resin transfer molding.The defects formation mechanism and effect factors are influenced by the variety and complexity of the fiber perform. With statistical analysis, the purpose of the study is to investigate void formation in multilayer woven fabrics which are always used in high-strength structures. Based on theoretical analysis, a basic model is established to study the void formation mechanism. The visual experiment and numerical simulation are used to validate the theoretical analysis and analyze the factors of the size of void. The results show that, for a given fiber perform, the permeability, the channel width, the width of fiber bundle and superposition mode are responsible for the void size.Resin injection through multiple gates has become a practical way of minimization of mold filling time without losing the part quality. But inappropriate injection methods lead to air entrapments, high inlet pressure and fiber mat deformation. The study is to analyze the effects of constant pressure injection, constant flow rate injection, gates and vents by numerical simulation. A processing parameter called maximum permissible injection pressure is introduced and resin injection at gates is switched from constant flow rate to constant pressure, leading to a low inlet pressure during filling process. The sequential switching injection and simultaneous adjusted switching injection are investigated. The results shows that switching injection method lead to maximum reduction in filling time, low inlet pressure and minimum numbers of vents.The study of this paper can enlarge considerably the area of application of RTM.