Heat transfer and crystallization modeling during compression molding of thermoplastic composite parts Jalal Faraj 1,a* , Baptiste Pignon 1,b , Jean-Luc Bailleul 1,c , Nicolas Boyard 1,d , Didier Delaunay 1,e ,Gilles Orange 2,f 1 Laboratoire de Thermocinétique de Nantes, UMR CNRS 6607, University of Nantes, rue Christian Pauc, La Chantrerie, BP 50609, F-44306 Nantes cedex 3, France 2 Solvay R&I Centre-Lyon, 85, rue des Frères Perret, F-69192 Saint-Fons, France a* jalal.faraj@univ-nantes.fr, b baptiste.pignon@univ-nantes.fr, c jean-luc.bailleul@univ-nantes.fr, d nicolas.boyard@univ-nantes.fr, e didier.delaunay@univ-nantes.fr, f Gilles.ORANGE@solvay.com Keywords: Thermoplastic composite, Crystallization, Heat transfer, Thermophysical properties, PA 66 Abstract. In this paper, we present the description of the coupling between heat transfer and the crystallization kinetics during the consolidation of a thermoplastic composite in a closed mold. The composite is based on thermoplastic resin (low viscosity PA 66) with glass fiber (50 vol% fraction). For computation purpose, an accurate characterization of thermo physical properties in process conditions, especially in the molten and solid state is needed. The identification of the parameters of crystallization kinetics is also required. We first present the methods used to study the thermo physical properties. Moreover, the kinetic of crystallization was estimated over a large temperature range by using both Flash DSC and classical DSC. In order to validate the measurements, the whole process was modeled by finite elements. Finally, the experimental and numerical results were compared. Introduction For the automotive industry, the manufacturing of a composite piece with complex geometry is a challenging task. Among the composite processes, liquid composite molding (LCM) is of high interest to produce such thermoplastic parts. In this study, we used a new generation of polyamide 66, which viscosity of the melt is around 15 Pa.s. This process must also be compatible with the requirements of cost, cycle time and quality. Therefore, it implies a significant reduction of cycle time, especially by heat transfer optimization. However, the quality of the parts strongly depends on the cooling phase when the crystallization of the thermoplastic matrix takes place. In this context, we designed an instrumented mold at laboratory scale allowing fast cooling (100 K/min) to study the heat transfer under conditions close to industrial ones. Thermocouples were located through the thickness of composite part in order to follow the evolution of the temperature. The thermal conductivity was measured by guarded hot plate measurements [1]. The resin heat capacity was characterized by using differential scanning calorimetry (classical DSC) method [2] and the resin specific volume was estimated by PvT-xT measurements [3]. Then, we have applied the mixing law to identify finally the heat capacity and the specific volume of the 50 vol% glass fiber composite. The crystallization of polymers is commonly restricted between the equilibrium melting temperature of crystals and the glass transition temperature. The study of the isothermal crystallization close to the glass transition temperature, is complicated since nucleation rate is very high at low temperatures. Therefore, it requires cooling at a rate which is distinctly higher than the maximum rate of nucleation. In fact, the cooling capacity of standard DSC is often limited to impose to the melt a high level of super-cooling before the end of the onset due to the stabilization of the temperature. For that reason, the Flash DSC 1device [4,5] was used, since the cooling rate can reach 10 4 Kelvin per second, which allowed to study the isothermal crystallization kinetics in a large temperature range.