Net-Shape Knitting for Complex Composite Preforms

Abstract

Net-shape weft knitting is used to produce preforms for complex shape composite parts, as illustrated by the wheel wells of the Sunrise all-composite electric ehicle. An integrated design for the manufacturing methodology links mechanical performance to cloth and stitch design. The use of drapable net-shape fabrics with tailored fiber rein forcement produced on automated knitting machines allows for a significant reduction in preform manufacturing costs. Net-shape two-dimensional knitted fabrics for the wheel wells are achieved by a combination of shaping techniques: holding, narrowing, widening. and binding off. An interlock stitch is chosen to uarantee sufficient mechanical perfor mance and to protect the brittle knitting yarn. The mechanical properties of the composites are studied, and the strength in the weak warp direction where only loope fibers are present is optimized by choosing a sufficiently larg loop size. In the weft direction, lay-in yams are tucked in to increase production speed.