Unconventional Machining Processes

Real Life Application- Due to the innovative nature and numerous material and machining benefits of pECM, the technology finds very wide cross-industry application. To current date, ECM Technologies have researched and developed for the majority of the high industries. It is normally used for mass production and is used for working extremely hard materials or materials that are difficult to machine using conventional methods. Its use is limited to electrically conductive materials. ECM can cut small or odd-shaped angles, intricate contours or cavities in hard and exotic metals, such as titanium aluminides, Inconel, Waspaloy, and high nickel, cobalt, and rhenium alloys. Both external and internal geometries can be machined. Explanation- Michael Faraday discovered that if two electrodes are placed in a bath containing liquid and a DC potential is applied across them then metal can be depleted from the anode and plated on cathode. Here, material is removed hence electroplating is reversed by making workpiece as anode. The metal from anode is dissolved electrochemically and hence, the MRR based on Faraday’s law will depend upon atomic weight, valency, current passed, and the time for which it was passed, and no other parameter. At the cathode only hydrogen gas is evolved and no other reaction takes place, so the shape of the cathode is unaffected. Thus the ECM process can now be conceived as a process involving a tool cathode, which has a complementary shape of the part to be produced and the work be made as anode. In the small gap between the workpiece and the tool, a suitable electrolyte is pumped at high pressure. The electrolyte has to be carefully selected such that they provide necessary reactions without plating cathode. Properties of electrolyte High electrical conductivity Low viscosity Chemically stable Non corrosive and non toxic Economical Examples- sodium chloride and potassium chloride, sodium nitrate. etc. Tool materials Common examples are- Aluminium Copper Brass Titanium Stainless steel etc.\ ECM parameters Current – 50 to 40,000 Amps Current density – 8 to 233 Amps/sq.cm Voltage – 4 to 30 V dc Gap – 0.025 to 0.75 mm Electrolyte velocity – 15 to 60 m/s Electrolyte pressure – 0.069 to 2.70 Mpa Electrolyte temperature – 24 – 65 deg C Feed rate – 0.5 to 19.0 mm/min Advantages Complex three dimensional surfaces can be machined accurately. Higher surface finish Longer tool life Limitations Use of corrosive media as electrolytes makes it difficult to handle. Sharp interior edges and corners are difficult to be produced. Expensive process. The material-removal rate(MRR) in ECM is given by MRR=AI/ZF kg/s The volumetric material-removal rate is given by dividing the above with the density of the workpiece material Where A=Atomic weight of the work material, I=Current, amperes Z= Valency of the work material, F=Faraday’s constant=96 540 coulombs, and ?_a=Density of work material The gap resistance R is given by Where ?=Specific resistance of the electrolyte h=Equilibrium gap and A_Gap=cross-sectional area of the gap
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