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#045 Electrolytic Etching - Electrolytic Honing

Category : Metal etching
June11, 2010

There is a process very similar to grinding called honing. This process uses oil grinding stones mounted to a retaining device called "hone". Applying pressure and rotary/reciprocating movements between the grinding stones and the work piece while injecting large amounts of kerosene or diesel, the work is processed. As compared to grinding, this process removes less material but the finished surfaces are extremely fine. This is applicable for final finishing of surfaces after grinding for precision parts.

Combining the mechanical honing outlined above with electrolytic etching is the electrolytic honing. The mechanism is shown in [Fig.1] below.

[Fig.1] Electrolytic honing system configuration

As can be seen in the figure, the work piece is the cathode, and the tubular metal tube tool is the anode. This tube tool is the equivalent of the hone in the mechanical honing, and is made of stainless steel for corrosion resistance nature. The gap between the two is maintained to 0.07mm~0.12mm and the metal tube is rotated and reciprocated. The tube has several slots that hold the bar/stick shaped grinding stones. The mechanism is configured similar to that of mechanical honing where the grinding stones are pressed against the work piece at a constant pressure.

The tubular cathode tool has a length enough to cover the entire process area during the reciprocating motion. There are many small holes provided laterally.

The electrolyte (normally a solution of NaCL) is supplied through the interior of the cathode tool, and flows out of laterally placed holes. When the rotary/reciprocating motion is applied to this arrangement with direct current applied, the grinding stones would remove small peaks on the metal surface while the etching action would keep fresh metal exposed, thus honing and etching actions are optimally combined.

Electrolytic honing, in comparison to mechanical honing, causes less wear on grinding media, causes no burrs, and leaves no residual stress and heat induced damages on fished surfaces. The electrolytic honing process uses relatively low current density of 20~45A/cm^2, while the pressure required to supply the electrolyte into the working gap is high at 10kg/cm^2. In some cases, better finish can be obtained by keep honing with grinding stones for several seconds after the electrical current is turned off.

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