Adaptive Control of Manufacturing Processes for a New Generation of Jet Engine Components

The manufacture of safety critical rotating components in modern aero engines is by nature very conservative. To achieve the required engine performance, thermal and mechanical stresses are pushed to the maximum, which in turn leaves the choice of materials to exotic super alloys. These materials are classed as difficult to machine under normal circumstances, but when added to the changes in mechanical properties which occur naturally from part to part, consequently variable and often unpredictable tool life, and the ever present possibility of random and unexpected process anomalies, machining processes can never be fully optimised. Stringent legislative controls are placed on safety critical component manufacture to ensure that parts entering service will function correctly and safely to a declared service life, and in declaring the service life for such a part, the machinability issues stated above have to be taken into consideration. Hence manufacturing process parameters are often reduced or tools are changed early to ensure part surface integrity. The industry method adopted, is to “freeze” to process following process qualification to first article inspection, and successful part validation via laboratory examination and testing. Once frozen, no changes to process parameters are permitted without time consuming and costly re-validation. In order to contribute to the solution of the above mentioned problems, aero engine manufacturers cn aim at improving their competitiveness by applying sensor monitoring and adaptive control techniques to the manufacture of their components. Being able to adapt the machining process to the constantly changing tool and component conditions whilst operating in a multi-dimensional “approved process window”, processes will be optimised to the prevailing conditions and no longer “frozen”. Benefits will be seen in terms of reduced part manufacturing process time, more consistent part quality in terms of geometry, surface and sub-surface properties, tool usage optimisation, elimination of costly part re-validation due to small process changes, and the possibility to improve component design due to optimised machined surfaces.