Non-destructive Evaluation of Manufacturing Anomalies in Aero-engine Rotor Disks

Manufacturing anomalies introduced during machining of critical parts, although rare in occurrence, have become a significant cause of gas turbine disk cracking events in the aero-engine. These non-geometric anomaly types are usually different to those commonly targeted by current production NDI efforts. A European Union funded programme 'MANHIRP' has been set up to address this issue by introduction of quantitative NDI results into probabilistic lifing concepts. A selection of the efforts undertaken to expand the capability of NDI is described in this paper. 1. Introduction: Rotor disk ruptures in aero-engines must be prevented with the highest possible probability. Statistics show that, although the aero-engine industry invests high efforts into quality assurance, manufacturing induced anomalies mainly caused by " rare events " are becoming the most important reason for disk failures. The international development programme " Integrating Process Controls with Manufacturing to Produce High Integrity Rotating Parts for Modern Gas Turbines " (MANHIRP), funded by the European Union, has been set up to address this issue. Engine manufacturers, institutes and universities from seven European countries are working together to investigate the most life limiting manufacturing anomalies. Three manufacturing methods producing the appropriate geometric features are under investigation: hole making (holes), turning (flat surfaces) and broaching (shaped slots). Commonly used NDI techniques as well as near term and longer term techniques are investigated to assess their potential for detecting and quantifying the most life limiting anomalies. In this paper these techniques are outlined along with some of the programme results and some open questions are posed. 2. Objectives of the NDI efforts within the MANHIRP Programme: During the first trials to create manufacturing anomalies, currently used production NDI techniques were applied to detect and quantify the anomalies, where possible. At this stage, eddy current and some optical methods were effective for detection of geometric anomalies, while etch inspection could detect some non-geometric anomalies. Following this, samples were metallographically cut up or fatigue tested to enable further characterization. The next step was to adapt so called near-term NDI methods, already discussed within the NDI community, to meet the needs of manufacturing anomaly detection. In addition, new inspection ideas were also investigated to determine whether the techniques were applicable or at least show promise, after further investigation, for use in future projects. However it was not the intention of the programme to spend the major effort on the development of new NDI techniques. 3. …