Modeling of spherulitic crystallization in thermoplastic tow-placement process: heat transfer analysis

An impingement heat transfer analysis is presented for hot gas torch heating in a tow-placement process of thermoplastic matrix composites. It is shown that experimentally available convective heat transfer correlations for normal and oblique impingement can be adapted to the geometry specific to the process by following first principles. Parametric studies are conducted using a coupled heat transfer and crystallization kinetics model for fabrication of a fiber-reinforced poly-ether–ether–ketone composite. Effects of processing parameters, in terms of torch incidence angle, θ, torch exit diameter, D, torch distance to target, L, hot gas temperature, Tnoz, gas velocity, Unoz, line speed, V, and number of layers in tow substrate, Nlayer, on the crystallinity development in product are elucidated. Based on an optimal level of crystallinity, a processing window is identified by determining minimum and sonic gas velocities at various gas temperatures and line speeds.