Powder mixed electric discharge machining-A review

Abstract

In current world scenario, there has been a steep rise in advancement of technology for progress of mankind, which has induced an urgent need to develop and adopt latest efficient methods for machining and manufacturing. Spark machining or Electro-Discharge-Machining (EDM) is known as the recent and upcoming advanced process for machining kinds of material in which electrical current can be conductive. In this technique, the machining operation is carried out due to the heat energy generated by the electric arc which is induced between the electrodes, generally tool termed as cathode and work material as anode. The machining zone is submerged in the circulating pool of dielectric fluid contained in machining tank. Powder-mixed EDM (PMEDM) is a variant of EDM process which involves suitable particles in form of powder, doped in dielectric fluid while machining. The use of powder added dielectric has resulted in enhanced machining of materials, including superalloys and composites. The process has been remarked to have improved the finish as well as the state of the machined surface and also decrease the solidified recast layer and white layer thickness. The modified state of the surface characterizations like increased micro-hardness and toughness, high corrosion and wear resistance were also observed. However, it has also been reported that very high concentration and size of powder had adverse effect on MRR and surface roughness (Ra). Hydrocarbon oils are generally used as dielectric in EDM, but led to pollution due to production of harmful hydrocarbon gases. Hence, bio dielectric like vegetable ester oils is effectively used as an alternate option to hydrocarbon oils. Also, rotating the tool was found to increase the machining rate and influence in lowering the surface roughness. MRR and surface characteristics can also be improved with use of ultrasonic assisted EDM where ultrasonic vibration is induced either to the tool or the workpiece or the machining tank. Further study, investigation and optimization of parameters is required on powder characteristics to render PMEDM commercially feasible.