Electrochemical Surface Finishing

Abstract

Electrochemical surface finishing is a highly scalable manufacturing process that traditionally uses viscous, non-aqueous and/or highly acidic electrolytes to achieve the desired surface profiles on metallic parts, with the addition of aggressive, hazardous chemical species to remove the oxide film on strongly passive materials. An emerging approach applies pulse and pulse reverse electric fields to control current distribution, mitigate oxide film formation and achieve the desired surface finish, in the presence of environmentally benign and simple chemistries. This approach lowers the cost of the manufacturing process, and improves process robustness. After a brief discussion of electrochemical surface finishing processes, case studies that describe deburring of automotive gears and electropolishing of semiconductor valves and superconducting radio frequency cavities are presented in this article. Conventional Electrochemical Surface Finishing Processes Electrochemical surface finishing removes metal in a selective manner from the surface of the workpiece by converting the metal into ions by means of an applied electric field. This is accomplished in an electrolytic cell by applying a positive (anodic) potential to the workpiece and a negative (cathode) potential to the tool used to shape the workpiece. While fundamental investigations of electrochemical metal removal processes typically employ a 3-electrode system, a manufacturing environment is typically not conducive to the use of reference electrodes. Therefore, most electrochemical manufacturing systems are based on a two-electrode cell. Conventional electrochemical surface finishing relies heavily on the “art” of chemical mediation for process control. Under the influence of a constant electric field and controlled electrolyte flow, aggressive chemical species diffuse to the electrochemical interface and control the preferential dissolution of asperities from a surface via an electrolytic reaction, which may be generally represented as: