Electrochemical grinding

Electrochemical grinding is a process that removes electrically conductive material by grinding with a negatively charged abrasive grinding wheel, an electrolyte fluid, and a positively charged workpiece. Materials removed from the workpiece stay in the electrolyte fluid. Electrochemical grinding is similar to electrochemical machining but uses a wheel instead of a tool shaped like the contour of the workpiece.

The electrochemical grinding process combines traditional electrochemical machining and grinding processes to remove material from a workpiece. A grinding wheel is used as a cutting tool as a cathode and the workpiece is an anode. During the process, electrolytic fluid, typically sodium nitrate, is pumped into the space between the workpiece and the grinding wheel. Other electrolytes used include sodium hydroxide, sodium carbonate, and sodium chlorate. This electrolytic fluid will cause electrochemical reactions to occur at the workpiece surface which oxidize the surface, thereby removing material. As a consequence of the oxidation which occurs, layers of oxide films will form on the workpiece surface, and these need to be removed by the grinding wheel. A couple schematics of the process are provided below.

Abrasive materials, either diamond or aluminum oxide, are bonded to the grinding wheel which allows the wheel to remove the oxide layers on the workpiece surface by abrasive action. Appropriate materials used for electrolyte fluid and the grinding wheel abrasives are summarized in the table below.

Sodium Carbonate, Sodium Chlorate

Most material removal is by the electrochemical reactions which occur at the workpiece surface. Five percent or less of the material removal is carried out by the abrasive action of the grinding wheel. The fact that most material is not removed by abrasive action helps increase the life of the grinding wheel, that is, the tool will take a long time to wear down. The electrolytic fluid serves another useful purpose - it flushes out leftover material in between the grinding wheel and work piece. The Abrasive particles bonded to the grinding wheel will help to electrically insulate the space between the grinding wheel and workpiece. An equation giving the material removal rate for an electrochemical grinding process is provided in and is stated here as:

MRR = GI/ρF

where ρ is the workpiece density, G is the total mass of the workpiece, I is the current supplied, MRR is the material removal rate, and F is Faraday's constant.

Some of the main factors which govern the performance of an electrochemical grinding process include current supplied, rotation speed of the grinding wheel, the workpiece feed rate, the type of electrolyte used, electrolyte feed rate, and the workpiece's chemical properties. By changing these parameters, one can alter the material removal rate. Increasing the supplied current, rotation speed of the wheel, electrolyte feed rate, or the workpiece feed rate will lead to an increase in material removal rate (MRR), while decreasing these properties will do the opposite. If the workpiece is more reactive to the electrolyte used, then the material removal rate will increase. The grinding wheel is usually rotated with a surface speed of 1200–2000 m/min and supplied currents are around 1000A.

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