Multiphysics Modeling Prediction of Electrochemically Machined Workpiece Geometries
Authors: Skinn Brian , Liu Danny X. , Moran Andrew , Hall Timothy D. , Snyder Stephen , Taylor E. J. 
Published: May 2020

Electrochemical machining (ECM) is a manufacturing technology that allows metal to be precisely removed by electrochemical oxidation and dissolution into an electrolyte solution. ECM is suited for fabrication operations using “difficult to cut” materials and/or producing parts with complicated and intricate geometries. In ECM, an electrochemical cell is established wherein the workpiece is the anode and the tool is the cathode; by relative movement of the shaped tool into the workpiece while applying a suitable electrical potential, the mirror image of the tool is “copied” into the workpiece. Compared to mechanical or thermal machining processes, where metal is removed by cutting or electric discharge/laser machining, respectively, ECM does not suffer from tool wear or result in a thermally damaged surface layer on the workpiece. Consequently, ECM has strong utility as a manufacturing technology for fabrication of a wide variety of metallic parts and components, and encompasses machining, deburring, boring, radiusing and polishing processes, among others. As noted, ECM provides particular value when applied to high strength/tough and/or work-hardening materials such as high strength steel, chrome-copper alloy (C18200), nickel alloy (IN718), cobalt-chrome alloy (Stellite 25) and tantalum-tungsten alloy (Ta10W), since the material removal process involves no mechanical interaction between the tool and the part.
One notable difficulty with ECM is an inability to predict a priori the tool and process parameters required in order to satisfy the final specifications of the fabricated part. Currently, most practical applications of ECM require an iterative prototyping process for tool development, where a succession of tools and parts are fabricated until the desired final form is achieved. In this talk, Faraday will present results from ongoing development work of a multiphysics-based design platform to predict optimal ECM tool shapes and processing parameters using commercial multiphysics simulation software. Simulation results for both an axisymmetric tubular tool and a non-axisymmetric tool fabricated by powder-bed additive manufacturing methods will be compared to experimental data gathered from ECM tests on various materials of commercial interest (alloy steel, nickel and titanium alloys). A notional non-axisymmetric tool, the electrochemically machined indentation obtained in an IN718 alloy plate, and the indentation predicted from multiphysics modeling are shown in the Figure. The effect of including selected physical phenomena in the simulations (kinetic polarization, surface occlusion by insoluble dissolution products, etc.) on the quality of the predicted machined forms will be discussed, and general guidelines for successful multiphysics modeling of ECM processes will be highlighted. Replacement of most or all of a costly experimental prototyping cycle with a more-rapid and less-expensive in silico multiphysics modeling like that described herein, along with enhanced ECM process performance [1-3] and simplified management of ECM electrolytes [4] through the application of pulse/pulse-reverse electrical waveforms, has the potential to significantly advance ECM as a mainstream manufacturing technology.

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.

References

[1] H. McCrabb, E.J. Taylor, A. Lozano-Morales, S. Shimpalee, M. Inman, J.W. Van Zee. “Through-Mask Electroetching for Fabrication of Metal Bipolar Plate Gas Flow Field Channels.” ECS Transactions, 33(1) (2010) 991-1006.
[2] E.J. Taylor, M.E. Inman, T.D. Hall, B. Kagajwala. “Electropolishing of Passive Materials in HF-Free Low Viscosity Aqueous Electrolytes.” ECS Transactions, 45(8) (2013) 13-20.
[3] H. Garich and T.D. Hall. “Electrochemical Surface Finishing of Additively Manufactured Parts.” ECS Transactions, 85(4) (2018) 155-166.
[4] B. Skinn, S. Lucatero, S. Snyder, E.J. Taylor, T.D. Hall, H. McCrabb, H. Garich, M.E. Inman. “Sustainable Electrochemical Machining for Metal Recovery, Elimination of Waste, and Minimization of Water Usage.” ECS Transactions, 72(35) (2016) 1-20.

Figure 1