DEVELOPMENT OF A MOLD FOR THERMOPLASTICS BASED ON A PHOSPHATE CEMENT

In case of limited series or prototypes of thermoplasts, metallic molds are too expensive and time consuming to build. For that reason, a production strategy was developed to build a textile reinforced phosphate based cement mold. The requirements are: stability up to 300°C with limited shrinkage/expansion, sufficient stiffness, and reduction of the permeability. In this research, a composite mold is developed, based on glass fiber textile reinforced phosphate cement (TRC). This tooling system is combining the advantages of a thermoset mold with elevated temperature use. Since cement based molding systems contain water, major challenges are the reduction of porosity, the sealing of the surface and the limitation of the thermal shrinkage. The development of an isothermal curing method resulted in a more stable P-cement, as confirmed by shrinkage measurements, X-ray Diffraction and Scanning Electron Microscopy. By adding fillers to the top coat, the surface permeability was decreased. The effect of thermal loading, composition of the matrix and the curing conditions were provided by an experimental study including acoustic emission. To illustrate the potential of the proposed method, a thermoplastic prepreg was processed in both the conventional metal and the TRC equivalent. The proof of concept showed that a textile reinforced cement mold can be used to thermoform a thermoplastic prepreg, to an acceptable part.