A new process for molding low density particulates, vented compression molding, is presented. Vented compression molding is a modification of standard compression molding that uses a perforated surface as the molding surface. The mold cavity is filled with an excess of material, which is forced through the openings in the surface of the mold as the mold closes. The resulting frictional forces, which can be determined approximately by a Mohr-Coulomb yield criterion, generate the pressure that compacts the material. Thus the pressure in the mold is 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. This uncoupling of the pressure-displacement relationship allows uniform material distribution and compaction without requiring large-scale flow of the particulates.

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