Heat transfer of fibre beds in resin transfer moulding: an experimental approach

Resin transfer moulding is a fibre impregnation process which is widely used for manufacturing of lightweight fibre reinforced plastic components for automotive and aircraft industry. For economic manufacturing of larger series of production lower cycle times must be achieved, thus injection strategies which allow a rapid infusion of the resin and impregnation of the fibres must be applied. For process optimisation numerical methods are increasingly applied to reduce time to market, cost and risk. Since temperature has an impact on flow and curing of the injected resin, heat transfer mechanisms between the tool and the uncured composite part is of major importance to achieve reliable numerical results. When fluid flows through stationary fibre beds, hydrodynamic dispersion plays an important role in heat transfer and is found to be a function of Peclet number. To understand the hydrodynamic dispersion phenomena, a test rig was designed to measure heat transfer at steady state conditions. The transverse effective diffusivity was investigated, whereas the influence of cavity thickness, porosity and resin flow velocity on effective thermal diffusivity was evaluated. Based on experimental data a model for heat transfer was developed. Because resin flows through a porous media, thermal diffusion is expected to be a combination of conduction and convection. Therefore the model for transverse diffusion for non-crimped fabrics was found to be a function of the thermal properties of the constituent materials, the fibre volume fraction, the degree of filling and the Peclet number. The model is suitable for all process stages, such as preheating, form filling and curing.