Electrical Discharge Machining of Deep Holes
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trical Discharge Machining of Deep Holes N. D. Oglezneva, *, S. A. Ogleznevaa, T. R. Ablyaza, **, E. S. Shlykova, ***, and K. R. Muratova, **** a
Perm National Research Polytechnic University, Perm, Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected] ****e-mail: [email protected]
Received January 17, 2020; revised January 17, 2020; accepted January 17, 2020
Abstract—The influence of the pulse energy in electrical discharge machining (EDM) of deep holes in 40Х steel workpieces is studied. The factors considered are the change in steel microstructure within the machining zone and the change in dimensions, shape, and surface roughness of the hole under the action of the current pulses. The depth of the defective layer in finishing and precision machining is no more than 1 mm. However, increase in pulse energy in the electrical discharge machining of 40Х steel is associated with increase in microhardness in the white layer and strengthening and increase in width in the tempering zone. Minimum pulse energy is associated with maximum precision and minimum surface roughness. Keywords: electrical discharge machining (EDM), piercing, microstructure, defective layer, tool electrode, dimensional error, surface roughness DOI: 10.3103/S1068798X20100196
Electrical discharge machining is widely used to produce deep holes in materials of great physical strength. It permits the creation of holes to a depth more than five times the diameter of the tool electrode, with high precision. The basic requirements determining the selection of the machining conditions are as follows: maximum productivity with specified precision and surface roughness; and maintenance of the microstructure and properties of the machined material in the machining zone. The productivity increases with increase in energy of a single pulse, which depends on the mean current and the pulse length. However, increase in productivity is accompanied by decrease in machining precision and increase in wear of the tool electrode [1]. In addition, increase in the local temperature is accompanied by vaporization of the machined material. On interaction with the working fluid between the electrodes, the metal vapor solidifies, producing slag [2, 3]. In machining with poor flushing of the electrode gap (in the case of deep holes, key slots, deep press molds, etc.), the erosion products collect in the machining zone, with the formation of secondary structures on the surface of the tool electrode. That impairs the product quality and productivity. The slag at the surface of the workpiece takes the form of spherical particles [4]. Those particles appear as a result of the cooling of metal vapor released from the workpiece under the action of the electrical pulse. Slag is also
obtained from the tool as a result of thermal crumbling. In the electrical discharge machining of deep holes, slag formation must be taken into account as a function of the pulse parameters. Thus, there is no consensus currently regarding how to assess the infl
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