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Electrochemical Machining of Turbine Engine Components


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials OBJECTIVE: Develop an electrochemical machining process which has lower up-front non-recurring engineering expenses while still enabling fast material removal for a reduction in machining times of turbine engine components and enabling more fuel efficient gas turbine engines. DESCRIPTION: Electrochemical machining (ECM) processes have been utilized for subtractive machining of aerospace materials such as nickel and titanium alloys. The process is particularly attractive due to its high metal removal rate in tough or heat-resistant materials common to the requirements of propulsion and power generation engines. The surface quality provided by ECM is also advantageous due to the low roughness and no heat affected zones or recast layer. In addition, the lack of electrode wear can lead to high process repeatability and lower production costs. ECM is relevant for a number of Navy propulsion needs, including compressor and turbine airfoils, integrally bladed rotors (IBRs) or bladed disks (blisks), cases, disks, and combustor components. IBRs and blisks, for example, are particularly expensive for 5-axis Computer Numerical Control (CNC) machining due to challenging materials (e.g., Ti6242, Inconel 718), tight geometric tolerances on 3D surfaces (e.g., +/- .001-.003”), and smooth surface finish requirements (e.g., =10 µin Ra). In addition, new IBR and blisk designs feature tighter blade-to-blade spacing, intentional mistuning, and thinner walls, which further increase costs for both new engine designs and Navy sustainment needs. These requirements increase the potential need for an ECM manufacturing solution. In addition, advanced designs are challenging the limits of current manufacturing techniques. Sharper leading edges, thinner walls, exotic tip geometries, and more complex curvatures can improve the overall engine efficiency or stall margins, but are more expensive, time consuming, or impossible to manufacture with conventional techniques. New material systems are being developed, such as titanium aluminides, high entropy alloys, and refractory alloys, which often have improved mechanical properties or heat resistance, increasing the challenge for contact-based machining processes and furthering the need for non-contact electrochemical methods. Finally, there is growing interest in near-net-shape processes, such as low-cost casting or metal additive manufacturing. In these cases, a secondary subtractive machining process is often necessary to improve final part tolerance and reduce surface roughness. To take advantage of the single-part nature of near net components, the subtractive manufacturing process needs the ability to access hard-to-reach areas, an area where ECM can excel. The low forces and insensitivity to material mechanical properties makes ECM a promising manufacturing technique to address all of these concerns, but its adoption has been largely limited to high volume commercial applications. The primary barrier facing greater adoption of ECM is the up-front non-recurring engineering expense (NRE) and process development costs. ECM is inherently inaccurate but repeatable, requiring iterations of the tooling to achieve the necessary accuracy. This iterative process of electrode design and process parameter selection is largely based on intuition and has limited its use to a few specialized firms, which rely on the knowhow and experience of its personnel. In addition, the tooling can be damaged by short circuit conditions during the testing phase, which damage the electrode and workpiece, leading to a time-consuming re-manufacturing process. Given these challenges, the United States Navy is seeking improvements to the electrochemical machining process which can: • Reduce the upfront tooling and NRE expense associated with current ECM processes • Yield cost and lead time reductions of > 25% for turbine engine components including fan, compressor and turbine blades, advanced casing treatments and combustor liners, when compared to current best practices • Be used for next generation metal material systems and geometries, including nickel superalloys and high entropy alloys • Promote the standardization of ECM procedures, accessibility to the machining method for lower production rates, and ECM workforce development PHASE I: Demonstrate proof-of-concept manufacturing of the improved ECM process on a relevant material system (e.g., Ti64 or IN718). Identify major risks to the proposed solution through analysis and/or experimentation. Identify solutions to the major risks. Test the proposed solutions on a representative geometry. PHASE II: Address the risks and challenges by modifying or improving the baseline manufacturing technique demonstrated in Phase I. Additional manufacturing demonstrations will be performed on representative propulsion engine components and materials. Demonstration components will be inspected to identify quality issues (e.g., metallurgy impacts, surface defects), geometric tolerances, and material removal rates. A cost model will be developed demonstrating a pathway towards 25+% cost reduction and identifying the total manufacturing process chain (i.e., proposed technique + pre- or post-processing steps), the capital equipment and NRE costs associated with the proposed technique, and the operating expenses of the proposed technique. PHASE III DUAL USE APPLICATIONS: Create a full-scale component using the developed manufacturing technique which could be used for further performance evaluation including rig testing, spin pit testing, or flow testing. If successful, this technology would have wide application in commercial advanced manufacturing for a variety of products. REFERENCES: 1. Xu, Z., Wang, Y.(2021). Electrochemical machining of complex components of aero-engines: Developments, trends, and technological advances. Chinese Journal of Aeronautics, Volume 34, Issue 2, 28-53. 2. Klocke, F., Zeis, M., Klink, A., Veselovac, D. (2013). Experimental research on the electrochemical machining of modern titanium- and nickel-based alloys for aero engine components. Procedia CIRP, 6, 368–372. .; KEYWORDS: Advanced manufacturing; electrochemical machining; compressor; turbine; jet engine; blisk; IBR; machining; surface finish
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