Numerical Analysis of Controlled Injection Strategies in Resin Transfer Molding

Minimization of mold filling time without losing the part quality is an important issue in the Resin Transfer Molding (RTM) process. Among the various methods to achieve this, resin injection through multiple injection gates has become a practical way. However, inappropriate injection methods lead to numerous air entrapments, high inlet pressure and fiber mat deformation. In this study, a processing parameter called Maximum Permissible Injection Pressure (MPIP) is introduced. This parameter is used as a constraint in all injection strategies utilized to study the mold filling process. A switching injection strategy at single gate injection is also proposed based on the concept of MPIP. In this strategy, resin injection at a specified gate is switched from constant flow rate to constant pressure, leading to a low inlet pressure during the filling process. According to the concept of switching injection, two different multiple gate injection strategies including sequential switching injection and simultaneous adjusted switching injection are investigated for complicated mold geometries. A computer code based on the Control Volume Finite Element Method (CV/FEM) is developed to study the mold filling process in all cases. The validity of the computer code used is checked by experiment and close agreement is found between numerical simulation and experimental observations. The results show that the simultaneous adjusted switching injection methods lead to maximum reduction in filling time, low inlet pressure and minimum number of vents.