In assemblies where contact to metal surfaces is critical, improvement of that metal surface becomes important. Virtually all metalworking operations including cutting, stamping, welding and forming roughen a metal surface. When that metal surface is then forced to work in critical sealing or friction zones, product performance often suffers.
One of the traditional instruments used to measure surface roughness is the profilometer. The profilometer, using a diamond stylus to record the irregularities of the surface, usually gives a readout in microinches or micrometers. This quantifies the roughness of the surface with a larger number indicating a rougher surface. Electropolishing typically reduces these microinch values by 50%, i.e. a 16 microinch surface before electropolishing will be improved to an 8 microinch afterward.
Illustration A depicts a typical cross-sectioned metal surface. The electropolishing process allows for a concentration of current in the peaks of a surface, thereby reducing microscopic peaks and causing a leveling action. By reducing the surface peaks, the microfinish values are reduced as well.
In general terms, electropolishing when properly applied can reduce microfinish values by 50% with a removal of .0005″ from each surface. Chart B (facing page) clearly shows that maximum benefit is achieved in this area, and that removing much more metal does not continue to improve surface finish.
It is important to note that electropolishing is best suited for improving microfinish values on complex or fragile parts. Many other microfinish improvement methods such as grinding, lapping or harperizing are not suitable on multi-faceted parts or fragile stampings.