Low-Cost Tool Design for Pulse-Reverse Electrochemical Machining of Aerospace Alloys via Multiphysics Simulation

Abstract

Electrochemical machining (ECM) is a manufacturing technology that precisely removes material from metallic workpieces via electrochemical means, typically oxidation, with subsequent dissolution/dispersal of the machining products into a working electrolyte. ECM is able to produce parts with complicated/intricate geometries, and is especially well suited for workpieces to be fabricated from “difficult to cut” materials, as no mechanical interaction occurs between tool and workpiece. In ECM, an electrochemical cell is established with the workpiece as the anode and a shaped tool as the cathode; a suitable electrical potential is then applied while the shaped tool is advanced into the workpiece, resulting in formation of a near-mirror image of the tool in the workpiece. Compared to mechanical or thermal machining processes, where material is subtracted by cutting or by electric/laser discharges, respectively, ECM does not suffer from tool wear or introduce a heat-affected zone to the workpiece. As a result, ECM has strong utility as a manufacturing technology for a wide variety of workpiece materials and ultimate part geometries, and encompasses machining, deburring, boring, radiusing and polishing processes, among others. As noted, ECM provides particular value when applied to high-strength/tough, brittle, galling-prone and/or work-hardening materials such as high strength steels, nickel alloys (e.g., IN718), titanium alloys (e.g., Ti-6Al-4V), cobalt-chrome alloy (Stellite 25), tantalum-tungsten alloy (Ta10W), molybdenum and tungsten.One challenge in practical execution of ECM is the tooling design process, which can require many costly and slow prototyping iterations and which often represents a significant barrier to entry for smaller manufacturing operations that might otherwise benefit from implementation of ECM. Multiphysics simulation has the potential to replace a significant fraction of the initial experimental prototyping effort with rapid, low-cost in-silico methods. This talk will present recent work by Faraday demonstrating a pulse-reverse ECM approach for fabrication of shaped Ni-alloy (IN625/IN718) and Ti-alloy (Ti64/Ti6242) workpieces, along with comparison of the experimentally-obtained results to simulated machined forms produced using the COMSOL Multiphysics® software package. For these preliminary simulation efforts, a 3D primary current distribution model was used to solve for the time-dependent electric field between a moving cathode tool and a workpiece surface, simulating deformation owing to metal dissolution. The simulated and experimental workpiece surfaces showed a satisfactory match for the complex, non-axisymmetric feature geometry embodying a notional form relevant to aerospace turbine and compressor blade manufacture, especially given the preliminary nature of the simulations implemented to date. A cost and lead-time analysis comparing a design process involving all-experimental tool prototyping iterations with one in which initial prototyping is performed computationally reveals the potential for significant cost/time reductions in the latter scenario. Thus, introduction of multiphysics modeling prototyping iterations to the tool design process has the potential to significantly reduce the barrier to entry for newcomers to ECM fabrication. Figure Caption Left to right: Non-axisymmetric tool fabricated by additive-manufacturing methods. Photograph and optical profilometry scan of indentation obtained by pulse-reverse waveform ECM. Indentation form predicted by multiphysics simulation. Figure 1