Pressure rise inside a cylindrical pultrusion die for graphite/epoxy composites
The pultrusion die, a fundamental component of the pultrusion process, is basically a cavity of the desired product cross-section and a means by which the composite material can be cured through the application of heat and pressure. In the pultrusion process, the pressure rise inside the die inlet can significantly affect the quality of the fabricated composite. The pressure rise in the die inlet helps in enhancing the fibre wet-out and suppressing void formation during manufacturing. A three-dimensional, axisymmetric model based on Darcy's law for resin flow through a porous fibre bed in cylindrical coordinates, which employs the finite volume solution method, was developed to predict the pressure rise in a pultrusion die for graphite/epoxy composites. A variable viscosity was employed, and an anisotropic permeability model was used for calculating the permeability values in the axial and radial directions. Various process control parameters including preform plate cavity to die cavity area ratio (compaction ratio), resin viscosity, pull speed, die heating profile, and fibre volume fraction were varied to investigate their impact on the die inlet pressure rise in the pultrusion manufacturing of graphite/epoxy composites.