Straightening methods for flexible T-profile rolling

Abstract

Varying material thicknesses along the longitudinal axis of stringer profiles in aircraft structures serve to reduce weight, a goal that is currently achieved through chemical milling. To introduce this thickness variation in a more environmentally friendly manner, a new flexible rolling process for T-profiles has been developed. The flexible T-profile rolling is based on a novel roll gap geometry that enables the simultaneous rolling of the web and flange of the T-profile. The rolls have varying radii, which leads to different longitudinal strains across the profile’s cross-section, causing vertical bow in the profiles. The objective of this study is to straighten the bow by three different methods: varying the thickness ratio between web and flange, varying the ratio between angular speeds of the rolls and using a straightening roll. The feasibility of these straightening methods is first tested experimentally. The straightening roll has proven to be the most robust and easiest to implement, though slightly less effective than ideally tuned methods. However, a residual bow remains in the profile due to the difference in longitudinal strain, which is why a combination of the various straightening methods is being investigated. To this end, experiments and numerical simulations are being conducted using extruded T-profiles made of Al7075 O.