Abstract: Apparatus is disclosed for making a hollow, rib-reinforced article from a composite preform of two thermoplastic sheets. One sheet has a pattern of ridges or grooves, on a surface which contacts the other sheet, to permit the free flow of fluid from a marginal edge to interior regions of the preform. The apparatus includes (1) a heater, (2) mold platens which include a rib-forming mold cavity, (3) a ram to close and hold the mold platen in contact with the composite preform, and (4) a manifold which supplies a pressurized fluid to a marginal edge of the preform, thereby distending the thermoplastic sheet into the mold cavity. Then, the ram is further closed to seal nondistended areas of the preform, forming a hollow, laminated article.

Abstract: The invention provides a process for preparing a hollow, rib-reinforced, laminated article by:A. placing two sheets between opposing mold platens, the sheets being aligned such that the sheet surfaces oppose each other, at least one of the sheets being a thermoplastic material heated to its thermoforming temperature and at least one of the sheets being provided with grooves or integral projections which form fluid passageways, and at least one of the mold platens being provided with a mold caivty to form a shaped article having ribs;B. closing the mold platens to contact the sheets; andC. introducing a fluid into the fluid passageways to distend the thermoplastic sheet into its mold cavity forming a shaped article having ribs, while the sheets maintain contact in the nondistended areas.