Electropolishing or electrochemical polishing (EP)

Electropolishing is a controlled and repeatable electrochemical process that removes metal from the surface of complex geometrical objects by means of electrolytic dissolution. Medical devices, stents,heart valve frames and surgical tools all depend on electropolishing to achieve the required surface finish for surgical applications.

EP deburrs and polishes simultaneously, revealing the underlying metal structure without any mechanical or thermal distortions, such as: scratches, tiny cracks, internal stresses, heat affected zones and unstable oxides. EP results in a smooth, microscopically uniform, bright and reflective surface.

The following high-magnification scanning electron micrographs show cobalt chrome and stainless steel devices before and after electropolishing:

Smoother surfaces minimize contamination buildup, facilitate better passivation, and reduce friction. These electropolishing benefits improve the biocompatibility of medical implants, by minimizing the foreign body response and the ability of bacteria to grow on the implant, while improving corrosion resistance.

NiTi implants, for example, require electropolishing to selectively decrease the amount of Nickel (Ni) on the surface and produce a thin passivating layer composed of titanium oxide. Nickel is harmful to the human body due to the carcinogenic and inflammatory reactions it induces. Therefore the benefits of electropolishing go beyond deburring, edge and corner rounding and smooth surface – improving corrosion resistance and biocompatibility is essential for biomedical applications.

 

Process variables

Electropolishing variables include: the object’s geometry, the underlying properties of the raw material, the initial surface finish (after cold working, laser cutting and heat treatment steps), the composition and saturation of the electrolytic solution, the temperature, the anode / cathode surface area ratio, the current density, the polishing time and the agitation method.