High-Speed Machining of Thin-Web, Large-Pocket Ti-6Al-4V Firewalls/Bulkheads

High performance aircraft structures have strict requirements regarding weight, strength and fatigue. The unitization of structures provides reduced labor costs, part count and improved quality while achieving desired weight requirements. Since firewalls are not part of the primary structure, they are typically made of built-up assemblies of thin plates, maximizing weight reduction. Chemical milling (CM) is used to create pockets however, this can be expensive, time consuming and environmentally unfriendly. Progress has been made in applying high-speed machining (HSM) techniques to titanium components via dynamic analysis, system stiffening and improved tooling. Yet application to firewalls is challenging since HSM can result in part distortion and unfavorable stresses not alleviated with shot peening. We will apply our innovative, scalable HSM process utilizing proprietary thermal management techniques in combination with machining modeling to V-22 firewalls. Teaming with Bell Helicopter, the monolithic design will result in dramatically reduced cycle time, cost, part count, and reduction or elimination of CM. The design of experiments testing will establish process boundaries and web thickness capabilities. Dynamic response analysis of the machine tool structure will identify appropriate stable process operating windows. Assessment of residual stresses and forces on part distortion will be made via model analysis.