Material Properties and Heat Transfer Parameters in Compression Molding of Glass Mat Thermoplastics
Abstract
The compression molding of glass mat thermoplastics (GMT) allows high volume manufacture of composite parts with a short production cycle. Computer simulation is often used to assist process development and optimization. Reliable simulation depends on input of material property parameters and accurate prediction of heat transfer. This thesis developed experimental methods to characterize material property and heat transfer process parameters. Results were obtained by applying the methods to a selected commercial GMT sheet. Heat transfer coefficients including convection coefficients during pre-heating and transfer, as well as contact conductance at sheet-mold interface were estimated by a parameter-fitting approach. Viscoelastic parameters of the composite were characterized by oscillatory torsion bar, which can be used to model the draping behavior. The elastic modulus and viscosity were fitted by a Williams-Landel-Ferry (WLF) and Cross-WLF model, respectively. Flow behavior of a stacked charge was also characterized by a 1-D squeeze flow model, where the apparent viscosity was fitted by a temperature dependent power-law model.