A case of reverse engineering for the manufacture of wide chord fan blades (WCFB) used in Rolls Royce aero engines

The paper describes the manufacturing process for wide chord fan blades (WCFB) and how the production of die sets used for their manufacture can be substantially improved using reverse engineering. Super plastic formed WCFBs are manufactured by diffusion bonding five separate blade pieces under high pressure. The blade is then hot creep formed into the required shape, using pressure to force the blade against the die walls to yield the desired form, blade twist and the honeycomb centre required. Two die sets are required, one for the hot creep forming of the blade billet and the second for the super plastic blade forming process. Their manufacture requires three solid models to be generated from a bespoke 'Fan Key System'. This calculates the die set geometry required for both hot and cold states. The three solid models comprise the casting model geometry which incorporates the draw angle and shrinkage allowance, the pattern model for the top and bottom die sets and a die set model used to define the NC part programs for the five axis finish machining process. The machining process has three elements, pre-machining sometimes termed water line or terrace machining, semi-finish and finish machining. Distortion caused by rate of cooling, graphite precipitation and mould dilation cause massive amounts of metal removal in the waterline machining process which can take up to 35h and is a non-value added process. It often leaves the die wall thin with the resulting effect on performance and life. A reverse engineering solution was used to improve the geometry of the castings by predicting die distortion more accurately. Point cloud models of nine casting sets were imported into reverse engineering software, 'Surfacer' which made possible a comparison with the surface geometry representation required. The resulting design information enabled more accurate die set design. Waterline machining had been substantially reduced and die life has been extended.