metrology software products (MSP) and Hong Kong Polytechnic University have developed a way to fully automate the machine tooling process. By increasing accuracy, this drastically improves what can be achieved within the machining process. At the time of this project, maintenance company Hong Kong Aero Engines (HAESL), a joint venture with Rolls-Royce, planned to use the method within its turbine blade refurbishment programme to improve repair rates and reduce scrap.
Aero-engine turbine blades are exposed to extreme temperatures during operation, resulting in deformation and distortion over time. After about 30,000 hours of air time, engines are entirely overhauled and the blades are taken out and repaired where possible, through metal deposition and machine tooling.
Around half of blades are, in theory, reclaimable, although the current yield is only around 80 per cent of this due to avoidable errors and poor practice, according to MSP. The company claimed it could increase that to a near-100 per cent level and completely reduce scrap. To achieve this, it worked with Hong Kong Polytechnic University and came up with a patented software system, called NC-PerfectPart.
“The major problem we identified was that many parts were being machined incorrectly because they were not located on the machine tool at the position they were supposed to be, through errors in fixturing or in built-up tolerances,” said Peter Hammond, Technical Director of MSP.
MSP probe the turbine and take the measurements into their software solution, which then optimises for position, distortion and material thickness. Using this, it then computes where the part really is on the machine and transfers this to the tool.
“The major factor is that we’ve taken all of the manual steps and interpretation out of the process,” says Hammond, “We can automate the measuring, the analysis and the uploaded accordance system; therefore we can automate the machining and reduce any scrap.”
At the time of the project, there were 16,500 Rolls-Royce engines in service and each engine has around 3,000 blades. On average, half of blades are repairable and, therefore, it is estimated that around 25 million blades will need to be refurbished at some point in the next decade.
Mick Brown, Operations Manager at HAESL, said: “We are very confident that this new application will greatly increase the repair yields of turbine blades when compared with today’s practices and, in doing so, reduce the cost of ownership for our customers, the world’s airlines.”
– A Czyzewski