Die-Less Forming of Large and Variable-Radii of Curvature in Continuous-Fiber Thermoplastic-Matrix Composite Materials

Abstract

Die-less forming is a method of forming complex shapes in continuousfiber thermoplastic-matrix laminates under only software control, i.e., without fixed dies. The "continuous" die-less forming concept for thermoplastic composite laminates has been extended to encompass (a) constant-curvature parts having curvature larger than the forming rollers, and (b) variable-curvature parts. Shape accuracies of 0.016" have been attained. Prior work with the same process indicates that aircraft quality (< 6 dB ultrasonic loss) can also be maintained throughout the operations. The key to good shape accuracy and quality is maintenance of a substantial (e.g., 25"C) temperature gradient from the main part of the forming zone to the tangent point where the material exits this zone. Manipulation of advective heat transport by proper selection of the forming velocity was effective in maintaining this temperature gradient. Key internal behavior which governs the shape accuracy includes adequate interply sliding within the forming zone and avoidance of plastic bending outside of it. This work contributes to methods for forming continuous-fiber thermoplastic composites to final net shapes without dies.