This paper discusses technological aspects of the combined metal stretch and superplastic forming/diffusion bonding (SPF/DB) process applied to the manufacture of large and structurally complex engine nacelle components of the C-17 Advanced Military Airlifter. The manufacturing approach uses the McDonnell Douglas four-sheet SPF/DB process as the principal fabrication method, which in combination with the concurrent stretch is perceived as the most innovative and technologically advanced concept undertaken by the industry.
The component is a compound curvature titanium 6AI-4V weld assembly made up of four, 20 mm (0.75 inch) thick sandwich segments approximately 90 cm by 120 cm (3 feet by 4 feet) in size.
Also addressed are the engineering and manufacturing concepts, quality criteria, and the need for, and challenges of predicting and controlling the SPF/DB process, a prerequisite for the economic viability of the technology.
Among the many fabrication steps, the purchase of the raw material to final inspection, the SPF/DB process is considered a critical process which in the context of this dissertation, implies that the quality of the product is solely dependent on the execution of the process itself.