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Automated Repair and Overhaul System for Aero Turbine Engine Components (AROSATEC)

Final Report Summary - AROSATEC (Automated Repair and Overhaul System for Aero Turbine Engine Components)

The maintenance, repair and overhaul (MRO) of aero engine components consists of a chain of different processes, e.g. inspection, de-coating / coating, welding, milling and polishing. Today, most of these processes are carried out manually.

Although the supply industry is developing improved machining equipment to automate the individual process steps, the single repair processes remain separate and unconnected. For example, the data which are acquired during the incoming inspection are often put down on paper and are not available in electronic form for subsequent repair operations. Even though the single repair operations may be automated, therefore, this does not improve the overall process by promoting data flow and factory automation throughout the entire MRO chain.

The project AROSATEC had to aim at two objectives. Firstly, to improve existing repair methods, by integrating adaptive machining technology. The adaptive NC technologies should make use of the information provided by a data management system and compensate for the part-to-part variation of the complex components to be overhauled. Additionally, the part-to-part variation due to the manual treatment would be eliminated.

A continuous data flow between the adaptive repair steps should optimise the single repair technologies as well as the efficiency and the flexibility of the entire chain of repair processes for aero engine components. Thus, secondly, a data management system which constitutes the core of the automated overhaul system for aero engine components has to be developed. As part of this innovative data management solution, the single repair process modules should be integrated to build an automated repair cell for aero engine components.

In the long run, the AROSATEC concept could also open the possibility to establish 'virtual' MRO workshops with the different repair steps carried out in remote countries. The data management system would generate a data set for each individual component and handle the logistics of the components and the accompanying data sets. As result, different MRO processes could be carried out at different facilities without loss of information, efficiency or quality. Work duplication could be prevented and the accuracy of the work carried out could be enhanced. In addition, the AROSATEC approach would support an efficient life cycle monitoring.

During the first half period of the project, especially the end user requirements were investigated. MTU and SIFCO defined the repair processes to be incorporated in AROSATEC, resulting in the detailed requirement specifications. These were analysed by the partners and compared to technologies already available. The gap between contemporary technology and requirements defined the development needs and goals for AROSATEC.

Besides setting up the detailed requirement specification, the scanning process and data-treatment optimisation started. In the course of AROSATEC, new scanners were tested and optimised, software interfaces were also optimised and adapted. Additionally, the general layout of the data backbone was set up and the concept was tested and verified.

The second year of AROSATEC was dedicated to optimise the different repair steps, from scanning to laser welding and to adaptive machining. While scanning improvements were made with use of new, high accuracy scanners, welding demanded sophisticated tooling, especially for complex geometries like on nozzle guide vanes, and intelligent welding strategies. A major problem for the adaptive machining was to find suitable fixture solutions and references to detect the positioning of the part automatically. Additionally, the data backbone was developed and improved.

During the third project period, the focus was upon integration of the processes and the adaptation of the data management. Fixtures for adaptive machining were successfully tested; also, the use of reference points and tactile measurement for automated high accuracy tool positioning was implemented. With the milling of the first blades also the adaptive machining part was completed successfully.

The AROSATEC process was set up successfully. During the income-inspection, the cleaned blades or vanes are inspected by the improved laser scanning technology. The laser scanner delivers a point cloud, a huge amount of discrete points on the surface of the scanned object. These points are a three-dimensional (3D) representation of the scanned part. To create a 3D triangular mesh, the data are triangulated. For the inspection, this geometry is then compared to computer-aided design (CAD) data were available or to accordingly digitised data from a master part. The comparison identifies and localises damaged areas on the surface of the scanned part. To have defined boundaries, the damaged areas are milled out. During the next step, material is added until the target shape is fully covered. This is done by build-up laser welding or laser cladding. Especially, the tip build up welding proved to be demanding and required testing of numerous welding strategies. Finally, a welding strategy was developed which delivered acceptable results. After welding, the part has to be milled. With milling, the nominal shape of the surface has to be restored. Thus, CAD data or nominal data from the master part and the geometry of the actual part need to be adapted to have a smooth transition between the surface areas. Additionally, precise positioning is mandatory. The positioning of the part and additional measurement points are taken with the help of tactile measuring. Milling and grinding complete the front end AROSATEC process.

The described process runs on the second - and probably most important - achievement of AROSATEC: the data backbone. Every individual step of the repair process uses and creates a data flow.

For every type of blade, nominal geometries are required, either from CAD or calculated based on the scanning of a new or unused master part. The nominal geometries serve as reference when calculating part to part deviations actually in charge. Every part creates a new set of data files, from the incoming inspection to the final inspection. The AROSATEC advantage is that these data files are generated once and can then be used in all relevant repair steps. The interaction between incoming and outgoing data is complex.

Especially, the question for a data standard had to be answered. This question turned out to be of major importance, as the data standard could limit the applicability of the AROSATEC process to certain machines / tools and thus could be counterproductive. The solution was found in XML, allowing the definition of open data formats which could serve directly as input file for machines as well as original for translation to specific formats. The greatest advantage of XML is the universal applicability, as it is set up in ASCII and could be read by humans and by machines.

Looking at more tangible results, every partner has identified ways of exploitation of AROSATEC. To sum it up, the new scanners developed in AROSATEC and the improved scanning strategies are already in use for other projects and are basis for further development. Also, welding solutions are employed for executing other tasks. The optimised milling strategies and new milling technologies will be used in succeeding projects as well as the XML-based program interfaces. Additionally, the ability to grind turbine shrouds was acquired and is expected to be offered to the market after some further refinement.

But what is most important is the way the AROSATEC industrial end users exploit the results: SIFCO, an aero turbine engine components repair shop, will utilise some of the adaptive machining processes improved in AROSATEC. To MTU, who also already have turbine blade repair processes, the AROSATEC data backbone and the data flow as developed during the project are the primary choice for exploitation and will be employed soon.

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