Technical and industrial approaches for super plastic forming and diffusion bonding (SPF/DB) titanium alloy leading edge manufacturing

The A330/340 HTP leading edge has shifted the prior composite into a new metallic design based on a SPF/DB manufacturing process for a two sheet D-nose. Superplastic forming and diffusion bonding were the technological means to obtain an integrated detailed part. Moreover, this component was part of the set that made introduction and development SPF/DB feasible within EADS CASA at its facilities located in Cadiz. The main driving factor to launch this program was the weight saving intended for the A330/340 horizontal stabilizer. The design concept was based on two raw material sheets (with initial nominal thicknesses of 3 mm and 0.8 mm) forming skins and spars. The skin was shaped into an aerodynamic nose and the flat spar was also stiffened by swages. It was diffusion bonded to the above mentioned skin by means of two flanges. The final shape is denominated by the term D-nose, due to the resulting geometrical configuration. The initial manufacturing process was based on a two step press forming process, with part integration as the main goal. This process was robust enough to achieve structural parts with industrial tolerance ranges. Since tighter tolerances ranges and higher than expected ramp up arose, creative improvements were set up to meet the program expectations. A single press forming phase was implemented, resulting in a lower press labour time and a higher quality product. Further increased mass production rates challenged the industrial means to reach higher efficiency. A compromise between part integration, costs and industrial means best practices has shown how detail parts assembly constitutes also a cost effective solution under specific industrial conditions. This article describes the advantages and drawbacks of three alternative SPF manufacturing processes to fabricate superplastic titanium alloys leading edges, which have been validated for mass production purposes.