Vented compression molding

A new process, vented compression molding, is developed for molding low density particulates, such as ablative materials used in the Space Shuttle. This process is a modification of standard compression molding that uses a perforated surface as the molding surface. An excess of material is used to fill the mold cavity and this material is forced through the openings in the surface of the mold as the mold closes. This process creates frictional forces, which can be determined approximately by Mohr-Coulomb yield criterion, generating the pressure that compacts the material. The pressure in the mold is shown to be governed by the geometry of the openings and the mechanical properties of the particulate, and not by the displacement or the volume of the mold. It is determined that this uncoupling of the pressure-displacement relationship allows uniform material distribution and compaction without requiring large-scale flow of the particulates.