Abstract
The thermoforming of thermoplastic sandwich structures based on the same matrix polymer for the face sheets and the core requires precise temperature control both before and during forming. Two opposing requirements must be satisfied: the face sheets must be heated to above the glass transition temperature of the polymer, Tg, whereas the temperature of the core should not approach Tg in order to avoid the collapse of the foam cells. A numerical model was used to determine the optimal thermal parameters for thermoforming using an inverse method. The conductivities of the skins, the interface, and the foam were first calculated by the inverse method and then implemented in a thermal analysis. It was shown that the thermal requirements for the skins and the foam cannot all be fulfilled using a classic one-step heating route; therefore, a two-step procedure was proposed. The numerical tool allowed the principal heating parameters, namely the temperature of the heating plates and the holding and transfer times, to be determined.