Experimental and numerical cure kinetics analysis of unsaturated polyester resin system using compression molding process

Abstract

This study aims to optimize the compression molding (CM) process for fabricating sandwich panels composed of polyurethane (PU) foam cores and woven glass fiber (GF) face sheets bonded with unsaturated polyester resin (UPR). The panels were produced through hand layup and consist of PU core, two GF fabric layers, and two thin skin liners of GF sheet molding compound (SMC). A novel integration of embedded thermocouples and thermography imaging was employed during the CM process to investigate the thermal gradient through the thickness of the panel. A thermo-chemo numerical model was developed and validated to predict the thermal distribution and cure behavior during the manufacturing process. Sandwich panels with total thicknesses of 1.5 in, 3.0 in, and 4.0 in were analyzed. The data showed that the top and bottom surfaces reached 140 °C after ∼12 min, while the center required ∼15 min. Heat transferred rapidly through the thin face sheets (∼0.05 in), whereas thicker shear-ties (1.5–4.0 in) exhibited slower heat propagation due to higher thermal mass, resulting in delayed temperature rise and extended curing times in the core. The validated model successfully captured the effects of both external heating and internal exothermic heat generation on the cure kinetics. Final average degrees of cure (DOCs) were 91.77 %, 87.01 %, and 84.14 %, respectively. The results show that while the faces cured within ∼15 min, the shear-tie regions required 3–5 h depending on thickness. This work present a robust experimental-numerical framework for analyzing and optimizing the cure behavior in thick UPR-based sandwich composites.