(Digital Presentation) HF-Free, Pulse-Reverse Electrochemical Machining of Tantalum

Abstract

Electrochemical machining (ECM) is a manufacturing technology wherein metal is precisely removed by electrochemical oxidation and dissolution/dispersal into an electrolyte solution. ECM is especially well suited for “difficult to cut” materials (high strength/toughness, work-hardening, etc.) 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. 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 voltage, the mirror image of the tool is “copied” into the workpiece. Production of parts with complicated and intricate geometries can thus be achieved in these challenging materials by design of a suitably-shaped tool made from a much more easily-machinable material. 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. Additionally, the use of pulse and/or pulse-reverse electrical waveforms can enable successful ECM of even highly passive materials using benign, HF-free electrolytes.Advanced materials such as refractories (e.g., W, Mo, Ta, and their alloys) provide highly desirable characteristics such as high strength, corrosion resistance, and survivability in extreme environments (high temperature, high chemical reactivity, plasma exposure, etc.). As motivation to adopt these materials has increased, conventional fabrication methods have proven progressively less able to successfully machine workpieces of the myriad needed geometries. ECM is a natural non-conventional fabrication method for these materials and workpieces, for the reasons described above. In this talk, we will present results from a proof-of-concept demonstration of pulse-reverse ECM of linear grooves in flat Ta and Ta10W alloy coupons using benign electrolytes, illustrating the potential for cost-effective, safe, environmentally-friendly fabrication using these exotic materials.