Internal Surface Finishing of Small Hole by Electrochemical Processing Using Soluble Fluid for Honing

Honing has been widely applied to engine cylinders, hydraulic cylinders, nozzles, valves and so on, since not only surface roughness but also roundness and straightness of a hole can be improved by this process. However, in the case of surface roughness less than 1μm Ry, a burr formed by abrasives significantly influences the surface roughness and makes it difficult to attain a better surface. In addition, the machining efficiency significantly decreases, since loading of the stick occurs frequently and several hones have to be prepared. In this study, in order to achieve high accuracy and efficiency in internal surface finishing with less surface roughness, the fundamental effects of electrochemical finishing after honing on surface integrity in the case of using a honing machine with soluble fluid as an electrolyte, are experimentally discussed.Experimental analysis clarified that a suitable electrolytic current density condition existed for improving the surface roughness, and also that passive film generation on the machined surface could be prevented by mixing inverse electrolytic current with the normal one. Then, it was pointed out that the surface roughness could be reduced, since only protruding parts were selectively removed under the suitable condition, even when a soluble fluid was used as an electrolyte. Therefore, this method has the possibility of being a highly efficient internal surface finishing process of small holes after honing.