(2) Acidic solutions

Various inorganic acid solutions have relatively high electrical conductivity, and there is no electro deposition risk on tool electrodes since cathode reaction is mainly of hydrogen discharge. However, the acidic solutions are typically highly corrosive and only used for special cases only.

In addition, when using the acidic solutions, the electrical conductivity becomes lower as the process progresses and the hydrogen is depleted. At the same time, the PH value increases and the metal ions are likely to electro deposit on cathode surfaces. The eluted metal ions will remain in the solution.

(3) Alkaline solutions

Normally, alkaline solutions are not used for most metals, since insoluble anodic products are generated and inhibit dissolution of work piece materials.

However, the alkaline solutions are effective for tungsten and molybdenum. These metals can firstly be oxidized by anodization, then tungstates and molybdates can be eluted using NaHO, and etc.

For these reasons, the alkaline solutions are used for electrolytic machining of cemented carbide material. Cemented carbide is essentially a mixture of tungsten carbide and cobalt, and they have different elution mechanisms. In order to obtain good surface finishes, at least two components that promote WC and Co elution. NaCL and NaOH are used for this purpose. Co is eluted with NaCL by Co+2CL > CoCL2+2e as cobalt chloride.

WC is first anodized into WO3, then reacts with NaOH as...

and eluted as sodium tungstate.

Alkaline solutions require care in handling but since they are non-corrosive to metals, selecting of component material for the processing system becomes very easy.

(4) Roughness of electrolytically machined surfaces

Since the electrolytic machining processes utilize electrolytic etching (elution) to remove an atom at a time from the material surfaces, mechanical forces and heat related effects typically associated with mechanical machining do not apply. Therefore, the resultant surfaces are different from that of mechanical machining.

Mechanical machining removes the material using contacting cutters that leave cutter marks, and that shows as the surface roughness, but non-contacting electrolytic machining does not. However, most metals are of polycrystalline in nature and each will have varying electrolytic elution speed, therefore some surface roughness will show.