PRESENTED BY ALBERT.N Under the guidance of Mr.N.RAMANUJAM M.E (Ph.d) (Associate Prof/Hod- Mech) DEPARTMENT OF MECHANICAL ENGINEERING E.G.S.PILLAY ENGINEERING COLLEGE NAGAPATTINAN

N.ALBERT

 Electric discharge machining is a thermo-electric non-traditional machining process  Material is removed from the work piece through localized melting and vaporization of material  It is the reverse process of “Electroplating”

Phases of Discharge  The discharge process during EDM can be separated into three main phases  The discharge process during EDM can be separated into three main phases Preparation phase Preparation phase Discharge phase Discharge phase Interval phase Interval phase

 The effect of various input parameters on material removal rate (MRR) and surface roughness (Ra) is discussed below  Pulse-on time  Pulse-off time  Flushing Pressure  Tool rotation

 The removal of material in electrical discharge machining is based upon the erosion effect of electric sparks occurring between two electrodes 1. Electro-mechanical theory 2. Thermo-mechanical theory 3. Thermo-electric theory 1. Electro-mechanical theory 2. Thermo-mechanical theory 3. Thermo-electric theory

 This theory suggests that abrasion of material particles takes place as a result of the concentrated electric field.  The theory proposes that the electric field separates the material particles of the work piece as it exceeds the forces of cohesion in the lattice of the material.  This theory neglects any thermal effects.

 This theory suggests that material removal in EDM operations is attributed to the melting of material caused by "flame jets".  These so - called flame jets are formed as a result of various electrical effects of the discharge.  However, this theory does not agree with experimental data and fails to give a reasonable explanation of the effect of spark erosion.

 This theory, best-supported by experimental evidence, suggests that metal removal in EDM operations takes place as a result of the generation of extremely high temperature generated by the high intensity of the discharge current  Although well supported, this theory cannot be considered as definite and complete because of difficulties in interpretation.

 The EDM setup consists of a power supply whose one lead is connected to the work piece immersed in a tank having dielectric oil.  The tank is connected to a pump, oil reservoir, and a filter system.  The pump provides pressure for flushing the work area and moving the oil while the filter system removes and traps the debris in the oil

 To flush the eroded particles produced during machining, from the discharge gap and remove the particles from the oil to pass through a filter system.  To provide insulation in the gap between the electrode and the work piece.  To cool the section that was heated by the discharge machining.

 Flash Point  Dielectric Strength  Viscosity  Specific Gravity  Color  Odor

 A signifficant number of papers have been focused on ways of yielding optimal EDM performance measures of high MRR, low tool wear rate (TWR) and satisfactory SQ.

The work material chosen for this experimental work is OHNS (Oil-Hardening Non-Shrinkable) die steel which is one of the most widely used die steel material for the manufacture of press tools; cutting dies and punches for blanking, trimming, flanging and forming operations. The work material chosen for this experimental work is OHNS (Oil-Hardening Non-Shrinkable) die steel which is one of the most widely used die steel material for the manufacture of press tools; cutting dies and punches for blanking, trimming, flanging and forming operations. The important characteristics responsible for the commercial popularity of this material are its ability to retain accurate dimensions at elevated temperatures, abrasion resistance, toughness and negligible deformation during the hardening process. The important characteristics responsible for the commercial popularity of this material are its ability to retain accurate dimensions at elevated temperatures, abrasion resistance, toughness and negligible deformation during the hardening process. It is commercially machined in the hardened state with EDM process using copper as the electrode material and kerosene as the dielectric medium. It is commercially machined in the hardened state with EDM process using copper as the electrode material and kerosene as the dielectric medium. The chemical composition of this work material is given in Table. No literature on the machining aspects of this material using any other electrode material or dielectric medium besides copper and kerosene could be found. The chemical composition of this work material is given in Table. No literature on the machining aspects of this material using any other electrode material or dielectric medium besides copper and kerosene could be found.

The electrical discharge machine (model Electronica – M2S) with Servo-head and positive polarity for the electrode was used to conduct the experiments. The electrical discharge machine (model Electronica – M2S) with Servo-head and positive polarity for the electrode was used to conduct the experiments. Commercial grade kerosene used as dielectrics and side flushing with a pressure of 15 lbs/in 2 was maintained for the whole experiment. The sparking voltage was fixed at 80 V and discharge current was varied from 4A to 15 A. In all, values of discharge current, namely, 15A, 12A, 10A,6A were used for Brass electrode material, and 10, 7A, 6A, 5A, 4A were used for Copper electrode material All the experiments were conducted with positive polarity of the electrode. Commercial grade kerosene used as dielectrics and side flushing with a pressure of 15 lbs/in 2 was maintained for the whole experiment. The sparking voltage was fixed at 80 V and discharge current was varied from 4A to 15 A. In all, values of discharge current, namely, 15A, 12A, 10A,6A were used for Brass electrode material, and 10, 7A, 6A, 5A, 4A were used for Copper electrode material All the experiments were conducted with positive polarity of the electrode. Besides discharge current, two other variables related to the spark pulse wave are on time and off- time which can be set independently. The diameter of crater formed during each spark is proportional to the applied current while its depth is proportional to the on- time. Besides discharge current, two other variables related to the spark pulse wave are on time and off- time which can be set independently. The diameter of crater formed during each spark is proportional to the applied current while its depth is proportional to the on- time.

 Two electrodes were machined to a cylindrical shape of 14 mm diameter and 50mm length  A plate of 200 mm ×60 mm size and thickness 18 mm of OHNS die steel was taken. It was subjected to a standard hardening cycle and it has a hardened at the range of 40 to 45 HRC  After mounting the work piece and one of the electrodes on the machine, the depth of machining was set at 25mm.

 Electrode material has a significant influence on important output parameters, such as, material removal rate, surface roughness and dimensional accuracy  Copper can be easily machined to any shape, suffers less wear, has good thermal conductivity, and is economical.  Brass is inexpensive and very easy to machine, but it has high electrode wear.

PROPERTYUNITMATERIALCOPPERBRASS Thermal conductivity W/m-K Electrical resistivity Ohm-cm Specific heat capacity J/g-deg C Melting point Deg C

ELEMENTCOMPOSITION,wt%Carbon 09 to 1.0 Silicon 0.3 to 0.5 Manganese 0.7 to 0.8 Chromium 0.5 to 0.6 Tungsten Vanadium1.0 IronBalance

Sparking Voltage (V) V80±5% Discharge Current (A) 15,12,10,8,7,6,5,4 Servo Control Electro Mechanical Polarity Normal (Electrode – Positive Dielectric fluid Commercial Grade Kerosene Flushing side Flushing with Pressure Work piece Material OHNS Die Steel (Hardened and Tempered) Electrode Material Copper and Brass