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TECH BRIEFS A Closer Look at Electropolishing Edited by Chris Felix lectropolishing has been evolving since the mid-20th century, when scientists frst started commercially treating metals with the combination of electricity and industrial chemicals. Since then, the process has grown more sophisticated, and now it can be used to make microscopic changes to metal parts. Electropolishing is often referred to as a "reverse plating" process. Electrochemical in nature, the process uses a combination of rectifed current and a blended chemical electrolyte bath to remove faws from the surface of a metal part. (and can be used for removing heat tint and oxide scale). Precise monitoring removes between 0.0001 and 0.0015 inch (per surface) to produce the desired result. Te typical electropolishing installation is deceptively similar to a plating line. A power source converts AC current to DC at low voltages. A tank typically fabricated from steel, and rubber-lined, is used to hold the chemical bath. A series of lead, copper or stainless steel cathode plates is lowered into the bath and installed to the negative E side of the power source. A part or group of parts is fxtured to a rack made of titanium, copper or bronze. Te rack, in turn, is fxtured to the positive side of the power source. Te metal part to be electropolished is charged positive (anodic) and immersed into the chemical bath. When current is applied, the electrolyte acts as a conductor to allow metal ions to be removed from the part. While the ions are drawn toward the cathode, the electrolyte maintains the dissolved metals in solution. Gassing in the form of oxygen occurs at the metal surface, furthering the cleaning process. Once the process is completed, the part is run through a series of cleaning and drying steps to remove clinging electrolyte. Te resultant surface is clean and bright. In fact, the bright surface is the most identifable trait, and the one that helped coin the name "electropolishing." Benefts While the process is best known for the bright polish left on the surface, there are some important, often overlooked benefts of this metal removal method. Tese benefts :: Although best known for the bright polished fnish it provides, electropolishing also assists in deburring, size control and microfnish improvement. 26 PRODUCTION MACHINING :: NOVEMBER 2013