The need for process modeling

Trial-and-error injections are still commonly used to achieve these goals in the industry. The locations of the injection gates and ventilation ports and injection boundary conditions are decided after these time-consuming trials. These injections require experience for iterating the boundary locations and conditions, and may not result in the optimal design. 

22 Delayed impregnation of the fiber bundles may cause entrapping microvoids in the bundles. Source Reprinted with permission from reference 1, copyright 2010 CRC Press,Taylor Francis Group.) 

Mathematical modeling of different stages of the RTM process has been applied for the last several decades to design the process. Flow, cure and mechanics models were developed to achieve the first three objectives listed earlier, respectively. In this chapter, flow modeling is discussed which allows the user to control the process parameters (resin injection pressure/flow rate) and design the mold (locations of the gates and vents). The details of the process modeling have been studied in many other books and book chapters. -  

The cycle time is the total of the three stages mold preparation and preform preparation, mold filling and resin cure. Mold filling time is predicted by using the flow models. Cure model is used to determine the degree of resin cure and if a database is available which relates the degree of cure to the mechanical properties, the user can decide when to demold the part. 

Flow and cure models require important material properties as input. These are permeability of the fiber preform and reaction kinetics of the resin, respectively. The accuracy of the models depends on the accuracy in characterizing these properties. 

---