Content area
Abstract
This work deals with the heat transfer aspect during the filling stage of the resin transfer molding (RTM) process when heated molds are used. This process is more and more popular in the automotive industry and in recreative transportation industries owing to its potential for overcoming the manufacturing difficulties involved in the processing of fibre reinforced plastics for medium to high volume production needs. The process can be described as a closed mold operation whereby a dry fibre preform is placed inside the mold and impregnated with a liquid, thermosetting resin. The resin is then cured and the mold opened to remove the component. Heated molds have proven to be effective in lowering the overall cycle time of the process by reducing the resin viscosity during the filling stage, allowing a faster impregnation of the fibre preform, and by reducing the cure time of the process due to higher resin temperature after mold fill.
A great deal of effort is currently devoted to the numerical modelling of such process which depends mainly on the physical and geometrical parameters involved during the flow of resin through the preform. The introduction of heat transfer phenomena in numerical models for RTM necessitates the use of an appropriate energy equation and of realistic boundary conditions. The present work deals mainly with experimental evaluation of heat transfer during the filling phase and, to a given extent, during the cure phase of the process. The results allow a critical evaluation of assumptions made in the governing equations and the corresponding boundary conditions used in the models for RTM.
Chapter 1 is a review of works made in the literature on the heat transfer aspect of liquid composites molding processes and on convection heat transfer for fluids flowing through porous media over a heated flat plate or between parallel plates. Chapter 2 deals mainly with in plane temperature variations during the impregnation phase of a flat aluminum mold. It is shown that about 70% of the resin temperature increase is obtained within a flow path length of 12.5 cm from the gate. Chapters 3 and 4 deal with through-thickness temperature measurements inside the mold cavity during the filling and curing phases and the influences of mold geometry and mold material on the temperature variations are investigated. Finally, chapter 5 is devoted to the evaluation of heat transfer models, as discussed in chapter 1, with a particular attention given to the possibility to use them as boundary conditions in the numerical models for RTM. By combining some of these models, a new model is developed for the RTM process where the influence of fibre content and mold temperature are taken into account.