On stamp forming of curved and flexible geometry components from continuous glass fiber/polypropylene composites

Abstract

A thermoforming technique known as stamp forming has been used to transform a pre-consolidated unidirectional glass fiber reinforced polypropylene (GF/PP) flat panel into a more complex geometry. To achieve this, firstly, two-dimensional half-tube composite parts were formed, mainly to optimize the processing conditions such as stamping temperature, forming velocity and mold geometry. The two-dimensional mold was kept at room temperature, whereas the composite panel to be formed was raised to a certain preheating temperature. The preconsolidated GF/PP panel, heated by contact heating in an external heater above the melting temperature of PP matrix, was then formed in the cold metal mold. Typical cycle times (including preheating and stamping) were in the range of 3-4 min. Secondly, a novel rod-bed mold was designed to manufacture three-dimensional parts using the same forming technique. Both halves of the mold were made of several tiny round metal rods in a metal frame. This rod-bed mold allowed to duplicate any solid contour by pushing it slightly on to the spring loaded rods. The final position of these rods could be fixed by forcing the side plates of the metal frame together. As an example, a saddle shaped, three-dimensional contour could be fairly well reproduced by stamp forming GF/PP composites with this rod-bed mold. The latter can have enormous potential in the manufacturing of medical devices such as adjustable prostheses or splints where only a limited number of parts with complex geometry have to be formed. © 1998 Elsevier Science Limited. All rights reserved.