This work presents the results of numerical simulation and experimental visualization of the mold filling process in resin injection molding with preplaced fiber mats. The mold filling experiments were conducted with various mat stacks consisting of continuous random glass fiber mats and bidirectional stitched glass fiber mats. The use of two different mat types in the mat stack created porosity and permeability variations. The effect of these permeability variations was studied by taking flow pressure measurements and observing the progress of the flow front of a non-reactive fluid filling a clear acrylic mold that contained the reinforcement mat stack. Numerical simulation corresponding to each experiment was also carried out. The numerical results were compared to the experimental measurements.

This work presents the characterization of fibrous reinforcement mats in resin injection molding. The fiber mat characterization involved determining the mat permeability and compressibility. Mold filling experiments were conducted using two or more different fiber types in the mat stack, which created transverse porosity, permeability, and compressibility variations. The effect of these variations was studied by taking flow pressure measurements and observing the progress of the flow front of a non-reactive fluid filling a clear acrylic mold that contained the reinforcement mat stack.

Non-isothermal mold filling and curing experiments of liquid composite molding were carried out in this work. To compare the experimental results with a previously developed numerical simulation model, measurements of volumetric heat transfer coefficient between the resin and the fiber, and characterization of resin kinetics and rheological changes were also conducted. Combined with the previously measured fiber preform permeability, the numerical model provided a good prediction of temperature profiles during molding for a polyurethane/glass fiber composite.

A numerical model for non-isothermal mold filling and curing simulation in thin cavities with preplaced fiber mats was developed based on the control volume method. Both lumped temperature system (i.e. local thermal equilibrium between the resin and the fiber) and unlumped temperature system (i.e. thermal non-equilibrium locally) were considered. A Lagrangian coordinate system was used in the flow front region to improve the energy transfer calculation. Several molding simulation results were presented to show the effect of fiber mat presence (in the mold cavity) on the inlet pressure and temperaturedistribution.

Means of reducing the flow-induced residual stresses in injection molded parts through optimization of the thermal history of the process are presented. A n approach through the use of a passive insulation layer with low thermal inertia on the cavity surface was investigated. The passive insulation layer prevents the polymer melt from freezing during mold filling and allows the flow-induced stresses to relax after the filling. The criteria for the optimal thermal properties and the required thickness of the layer are presented. A numerical simulation model of non-isothermal filling and cooling of viscoelastic materials was also used to understand the molding process and to evaluate this approach. This model predicts the stress development and relaxation in the molding cycle. Both simulation and experimental results show that the final stresses in the molded parts can be reduced significantly with the use of a n insulation layer. This technique can also be applied to other molding or forming processes in order to decouple the material flow and cooling process for minimum residual stresses in the molded parts.