Hot Drape Forming of Aerospace Structural Parts

Abstract

Cost-effective manufacturing of high quality aerospace composite parts can be achieved through new part design and integration as well as through manufacturing process automation. Automated technologies such as tape or fiber placement can be used to make large flat uncured panels to be shaped to the structural parts such as stringers, ribs and other types of stiffeners. Hot drape forming is a process for forming a flat uncured thermoset composite prepreg laminate (or thermoplastic perform) into a straight or curved angle or channel, using heat and pressure (vacuum). During this process in-ply shear deformation (for fabrics) as well as interply slippage must occur. The heat applied during process reduces the resin viscosity and therefore the interply shear. The pressure provides the mechanical action to form the laminate. Part geometry, ply orientation, flange length, temperature, and forming rate are variables that significantly affect hot drape forming process. The major challenges associated with this process are consistently creating components with very high uniformity of fiber content and fiber alignment, while avoiding wrinkling or uncontrolled fiber breakage. Ply wrinkling (buckling of fibers), fiber misalignment, fiber volume fraction variation and thinning at the radii are the common problems. Processing windows has to be defined to achieve a good quality part at the end of forming operation.