Compression moulding of thermoplastic composite sandwich components

Abstract: The thesis investigates various aspects of compressionmoulding of sandwich components with thermoplastic-basedcomposite faces and thermoplastic or thermoset core.Compression moulding of glass/polypropylene (PP) faces toexpanded PP core is initially experimentally investigated usinga statistical experimental design approach. The influence ofvarious processing parameters is evaluated in terms of theshear, flexural and transverse tensile properties of mouldedcomponents. Results indicate that as long as the faces remainmelted when stacked with the core, the face-core bond strengthis always greater than the tensile strength of the core. Ingeneral properties seem to improve with reduced mouldingpressure and time.Bonding of thermoplastic composite faces to a thermosetclosed cell foam core is then modelled assuming that there is acorrelation between the amount of matrix penetrating into corecells at the surface and the bond strength. The model is usedin a parametric study showing that matrix penetration into corecells is initially a rapid process, but flow is interruptedbefore cells are filled owing to increasing pressure of the airtrapped in the cells. The model indicates that increasedmoulding pressure and reduced face temperature increase matrixpenetration into core cells. Initial experimental resultssupport model predictions.Compression moulding of thermoplastic composite faces to athermoplastic honeycomb core is also modelled focusing on theface-core bonding. A process model is developed from modelsdescribing the temperature distribution in the sandwich and theflow of the melted part of the core wall during moulding. Modelpredictions are compared to experimental data in terms of faceand core surface temperature and degree of face-coreinterfacial contact with reasonably good agreement. The modelis also used in a parametric study investigating the influenceof the major process variables on the face-core bondstrength.Finally, the process economy of compression moulding ofthermoplastic composite and sandwich components is modelled andcompared to predicted component costs for compression mouldingof sheet moulding compound and stamping of metals. A range ofcomponent sizes, complexities and flexural rigidities isinvestigated. The results imply that thermoplastic compositecomponents are mainly cost competitive for small to mediumsized or highly complex components and for short productionseries. Sandwich components seem to offer enhanced processeconomy for components requiring high flexural rigidity,however, still for short to intermediate production series.Keywords: sandwich, thermoplastic, composite,compression moulding, modelling, bonding, heat transfer, matrixflow, cost, testing