An integrated adaptive machining process for the repair of aeronautical components

Abstract

There is an increasing demand for the development of automated repair strategies for aerospace components. Compared with the high cost of purchasing new components, the cost of repairing used ones is much lower. Due to the foreign object damage, high-cycle fatigue, corrosion, wear, etc., various kinds of deformation of the used components are exhibited. A single general repair process is not feasible for the maintenance or restoration of those worn and deformed parts. The ideal advanced machining process to repair aeronautical components according to their unique shapes, with a quick turn-around time and high precision, should be automatically controlled by computers with only a few manual operations needed. Such fully automated process, also termed adaptive machining process, is hot research topic in the maintenance, repair, and overhaul (MRO) industry. This research presents a novel adaptive machining approach to restore the critical shape of the thin worn leading edge (LE) of the large size wide chord fan blade (WCFB) based on reverse engineering. For high overall efficiency, this study adopts the contact on-machine measurement approach which hybrids the function of surface measurement and machining. The advantages are the elimination of repeated operations of blade movement and orientation saving time and preventing positional differences between measurement and machining, ensuring high machining accuracy. An adaptive and automatic machining process has been developed in this study. The developed algorithms control the workflow based on the calculation result of each step. The restoration of the LE is constructed from the mathematical models. The innovative points of this study are the establishment of new mathematical models of the LE for the measurement of both full radius and non-full radius profiles, high efficiency algorithms for presenting the reconstructed profiles parametrically and three dimensional models, highly adaptive workflow algorithm to control the movement of the machine without using master model as a reference, easy operation fixture for large size freeform aero engine components with thin edge, and an integrated automatic system requiring very limited manual operation. The repaired Trent 800 fan blades were sent out for independent verification by third parties. The results of better than 3 microns prove that the repaired part has high surface continuity and smoothness. The check points requisite in the maintenance specification of the Trent 800 fan blade are complied with fully. The adaptive automatic process enhances the efficiency, accuracy, and reduces cost for the repair of the LE of the WCFBs. The engine manufacture Rolls-Royce is prepared to take the above process onto the production floor. It will bring great benefits to the aviation industry.