Welded Aluminium Nose Cone & Boattail: Manufacturing-Ready Design

A demonstrator rocket programme needed a welded aluminium nose cone and boattail that could go straight from design into the workshop: formed from sheet, joined by hand-executable welds, and light enough to meet strict mass targets, all without the benefit of the raw material forms or tooling available to a larger aerospace prime. The brief evolved from an open design study into a fully detailed manufacturing package, driven throughout by direct, iterative dialogue with the manufacturing team who would actually build the parts.

The guiding philosophy was that a design is only as good as its manufacturability: every geometric decision, from the number of panels to the weld joint style, was made by weighing structural performance against what a metal-forming and welding shop could realistically and repeatably produce.

The project began with a manufacturing trade-off study comparing a multi-frustum construction (multiple shorter cone segments welded end to end) against a single-frustum approach where the whole nose cone profile is formed as one continuous developed surface, split only longitudinally into panels. The single-frustum route was ultimately selected: eliminating every circumferential seam removed a whole category of alignment and weld-inspection risk, reduced total part count from over a dozen pieces down to four panels, and gave a cleaner, more continuous load path through the skin. That decision came with a real trade-off — forming a compound-curvature profile as one continuous piece asks more of the rolling process than a series of simpler segments — and the design responded by leaning on additional internal ring stiffening and closer ring spacing to keep the formed panels true to shape through assembly, rather than treating the forming challenge as someone else's problem to solve downstream.

Material selection followed the same manufacturability-first logic: AW-5754 was chosen primarily for its weldability, allowing the extensive plug-weld and longitudinal-seam joining scheme without post-weld heat treatment or the hot-cracking risk of higher-strength alternatives. Its structural properties were adequate for the operating loads at practical sheet gauges, but the deciding factor was that it let every joint in the design behave predictably during welding — a case of choosing the material to fit the manufacturing process rather than the reverse.

The joint architecture itself was built around a lap-strip-and-plug-weld system: adjoining panels overlap onto an internal backing strip, with plug welds penetrating through both panel edges and the strip beneath, producing a strong longitudinal seam with no visible external weld bead. Internal stiffening rings followed the same principle, attached from outside through small access holes so that every structural connection in the assembly could be made without exposing a continuous external weld line — preserving a clean aerodynamic surface while keeping the joining process itself straightforward and repeatable.

Structural adequacy of this welded, ring-stiffened shell was confirmed through FEA covering combined aerodynamic pressure and handling/transport load cases, checking both static stress and buckling stability of the thin formed skin under the internal ring layout — validating that the manufacturability-driven geometry was also structurally sound, rather than treating structural sizing and manufacturing strategy as sequential, disconnected steps.

The project's final deliverable reflected this manufacturing-first philosophy throughout: a complete package of DXF flat patterns for every formed panel and ring, ready for direct use in sheet metal cutting and bending, accompanied by manufacturing drawings carrying explicit weld callouts (joint type, hole spacing, applicable welding standard, and required inspection method) for every seam in the structure. Rather than handing over a CAD model and leaving interpretation to the shop floor, the package was built so that cutting, forming, and welding could proceed directly from the drawings with minimal ambiguity.