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#039 Electrolytic Etching - Electrolytic Grinding - 1

Category : Metal etching
April23, 2010
(1) Principle of electrolytic grinding

Electrolytic machining is a method of removing material from metal surfaces by electrolytic etching, and electrolytic grinding is a process that adds mechanical grinding process to this.

Typically, with the electrolytic elution processes, some anodic byproducts that inhibit the elution will be formed and in some cases the elution can completely stop due to the metal surface becoming passivated. In order to prevent this, non-passivating solutions are selected for electrolytic machining. In contrast, the electrolytic grinding employs mechanical grinding by abrasive grinding media to scrape away the passivated layer so the etching process can continue on to the freshly exposed metal surfaces.

Electrolytic grinding was originally developed for grinders to produce electrolytic machining tools, but eventually was widely applied for many hard-to-grind materials since the method offered lower grinding heat and forces in comparison to the conventional methods.

(2) Grinding wheel electrode

In electrolytic grinding, the total amount of material removed can be divided into the amount removed by mechanical grinding and electrolytic elution. The amount removed by the mechanical grinding is very small as 1~2% for carbon steel, and 10~16% for carbide, while most material removal is by the electrolytic elution. [Fig.1] shows the cross section view of the grinding wheel.

[Fig.1] Cross section view of grinding wheel

The grinding wheel is composed of non-conductive abrasive particles and binder material (mostly metallic). The non-conductive abrasive particles protrude by a small amount (typically 0.02~0.05mm) from the surface of the conductive binder material. The insoluble anodic byproducts on the surface is ground off by the abrasive particles to allow the conductive binder material to continue the electrolysis on freshly exposed metal surfaces. This also sets the machining gap.

(3) Electrolytic grinder system

[Fig.2] shows an example of a electrolytic grinder system. Electrical current flows from: positive side of the DC power supply > work table > work piece > electrolyte (working gap) > brush > negative side of power supply. The electrolyte is sprayed onto the frontal surface of the wheel, then the centrifugal force of the rotating wheel feeds the electrolyte into the working gap.

[Fig.2] Electrolytic grinder system

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