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 with exotic super alloys. These materials are classed as difficult to machine under normal circumstances, but when added to the changes in mechanical properties, machining processes can never be fully optimised.
Stringent legislative safety controls are placed on critical component manufacture to ensure that the parts entering service will function correctly and safely to a declared service life. 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 then 'freeze' the process following process qualification, first article inspection, and successful part validation via laboratory examination and testing. Once frozen, no changes to process parameters are permitted without a time-consuming and costly re-validation. Validation of new manufacturing methods (or even an adaptation of an existing method) can easily exceed a timeframe of two to four years.
ACCENT allows the European aero-engine manufacturers to improve their competitiveness by applying 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, the elimination of costly part re-validation due to small process changes, and the possibility to improve component design due to optimised machined surfaces. Anticipated cost savings could be up to 40%.
The project was divided into five work packages (WP).
WP1: Project Management.
WP2: Ensured that a standard procedure was generated to define multi-dimensional parameter windows for the machining process and material combinations. The outcome was a specification which defines how a machining process has to be established and controlled in order to satisfy a defined surface integrity level.
WP3:Focused on developing the Standard Procedure for Adaptive Control. The work package set out to deliver an understanding of how to use process monitoring systems in a closed-loop adaptive control system that keeps the process within a defined process window.
WP4: Brought together those elements that have a direct effect on the component performance in terms of life and fitness for purpose. The interaction between the surface integrity generated as a result of the machining process parameters, cutting tool and machine tool condition, material characteristics, etc. will be investigated and understood.
WP5: Exploitation and Dissemination.
The knowledge gained here will allow the design function to understand the effect of machining processes on part quality and subsequent component service, and thus allow the component design to be optimised. With the new validation procedure, new demands will be placed on storage and retrieval of related data.
For the manufacture of critical aero-engine components, ACCENT developed a standard procedure for defining process parameter windows and develop methods whereby components manufactured within these process parameter windows are validated to meet the demands of design and surface integrity requirements. It provided a new manufacturing methodology that will allow for a significant reduction in recurring validation costs and develop a novel standard procedure for adaptive control based on process monitoring techniques. It took account of factors responsible for producing variable part quality and provide aero-engine manufacturers with a methodology that can be adapted to individual company procedures, thus allowing the design and manufacture of critical components to be optimised. As the majority of Europe's aero-engine companies are project partners, increased contacts will lead to new collaboration opportunities and consolidation of the aero-engine sector in Europe. ACCENT involved world-leading experts from both universities and companies in Europe, thus helping to in
Partners successfully demonstrated the ACCENT concept using an expanded process parameter window and adaptive process control to machine the alloy (Inconel 718). Complex-shaped slots in turbine discs (broaching) were manufactured. Along the way, project-related research supported nine doctoral dissertations, nine master theses, and led to 25 publications in European and international journals and conferences. Furthermore, excellent cooperation resulted in a complete list of surface features and anomalies, as well as guidelines on methodologies for surface integrity examinations.
ACCENT brought together leading European aero-engine manufacturers and university research groups to enhance the competitiveness of safety-critical component production. Advances in process monitoring and control enabled a demonstrated decrease in manufacturing costs with a simultaneous increase in component quality. Partners and end users are currently benefiting from implementation, and cooperation with the European Aviation Safety Agency (EASA) could facilitate standardisation in the future.
ACCENT technical and scientific field of new experience, progresses and results:
- Modelling & monitoring of machining(milling) operation
- Expertise on broaching trials and fundamental project
- Hard material behaviour in turning and hole-making
- Hard material surface integrity analysis after turning and hole-making
- Hard material process monitoring strategies for drilling and turning
- Modelling monitoring of milling operation
- Hard material surface integrity analysis after expertise on turning and milling trials
- Adaptive Control Solution for Milling of Inconel718 with Principal Component Analysis
- Hard material process monitoring strategies for turning milling
- Residual stress condition and measurement on milling of Inconel 718
- Machining of titanium and nickel based alloys knowledge
- Various statistical analyses and data processing applied to experimental results
- Area of artificial neural network application of tool wear and surface roughness modelling, and prediction for drilling, milling and turning operations
- Knowledge on turning of Inconel based on surface integrity data
- Process monitoring strategies for turning of Inconel operations
- Turning of Inconel718 knowledge
- Multiple sensors system for monitoring of turning knowledge
- Tool wear detection and measurement for turning of Inconel718 operation
- Residual stress condition and measurement on turning of Inconel 718.
An efficient and integrated mobility system:
- Service quality and reliability