COLLAPSIBLE, COILED MANDREL

A collapsible, coiled mandrel (40), for use in co-curing of a hollow carbon-epoxy structure such as a stringer (16) in aircraft construction, is made of a fiber (48) stiffened with doping material (49) that maintains an outer coil shape (28) resistant to external compression forces when used as a mandrel during lay-up and curing, and is collapsible when an end of the fiber (48) is pulled along its longitudinal axis so that it can be easily removed after curing and discarded. A method of fabricating a collapsible, coiled mandrel (40) employs a mold with a shaped recess for forming a coil with a fiber (48) wetted with a doping material (49) fed in by an applicator (54), and rotating the applicator (54) while backing it out to form the coil (42) in the mold. In an alternative embodiment, a collapsible, coiled mandrel (40) may be formed of a metal coil having a mandrel-shaped cross section and sleeved in a protective liner (44).