Blisk Production of the Future - MTU Aero Engines

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ECM premachining PECM finishing Figure 14: Blisk manufacture by a combination of ECM premachining and PECM finishing – airfoil geometries and surfaces. 3.2.4 Shot peening Most of Blisk blades are subject to controlled shot peening to increase their fatigue strength. Alongside conventional shot peening MTU Aero Engines uses ultra-sound assisted shot peening which offers the advantage of minimum component distortion, since both airfoil sides are normally compacted simultaneously. schematic Figure 15: Test setup for US shot peening Part Peening Chamber Sonotrode Piezo Shaker Controller + Amplifier SONATS Figure 16: Principe of US shot peening Conventional shot peening Intensity: 0.2 A, coverage: 125 % US shot peening Intensity: 0.2 A, coverage 150 % 250µm Figure 17: Comparison of the surface texture achieved by a) conventional and b) US shot peening Since US shot peening does not increase the roughness of the airfoil surfaces, in particular in the leading and trailing edge areas, postpeening finishing processes that had to be performed after conventional shot peening are no longer required.
3.2.5 Quality assurance In this area, optical measuring techniques hold promise of time savings and more reliable quality statements as compared with conventional measurements using coordinate measuring machines (CMM). In contrast to conventional assembly of rotors, the manufacture of blisks is subject to particularly stringent requirements in terms of airfoil location, radius and airfoil profile tolerances. Depending on the stability of the manufacturing process used, therefore, extensive dimensional inspections must be performed in the course of in-process and final inspection. Compared with the tactile systems used on CMMs today’s advanced optical systems offer great potential of reducing the inspection effort. They need far less time to provide complete models of the components which can then be verified by means of computation routines, for example to assess manufacturing deviations in boundary cases. In cooperation with the measuring system manufacturers, MTU Aero Engines has succeeded in improving the accuracy of the systems also for dimensional inspection of leading and trailing edges, for example. Figure 18: Dimensional inspection of a blisk Figure 19 : Leading and trailing edges inspected using optical systems 3.2.6 Repair Due to the integral construction of blisks a variety of repair processes needs to be modified or newly developed. Repairs that go beyond the scope of blending, a standard repair method also for individual blades, involve processes, such as buildup welding or patching that call for perfectly matched process steps, particularly when recoating or subsequent heat treatments are required. Repair processes Figure 20 : Repair categories A, B, C, D Of the repair categories illustrated above, the replacement of complete airfoils poses the most exacting requirements, as this repair involves the use of cutting and joining processes in the vicinity of critical component zones. Category A to C repairs are already used at MTU AERO ENGINES, category D is being developed. 4. Future developments 4.1 New designs The blisk design having become state-of-theart in the entire compressor area, including the high-temperature-resistant high-pressure compressor stages, MTU Aero Engines is now working on the development of fabricated, high-stressed low-pressure turbine blisks. Unlike with the smaller, integrally cast variants used, for example, in auxiliary power units (APUs), the special challenge to be overcome here in manufacturing is the material mix of forged disks and high-temperature cast blades and even single-crystal materials. Figure 21: Design example of a fabricated turbine blisk
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Blisk Production of the Future - MTU Aero Engines

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