PRESENTED BYPRESENTED BY

ALBERT.NALBERT.NUnder the guidance of

Mr.N.RAMANUJAM M.E (Ph.d)

(Associate Prof/Hod- Mech)

DEPARTMENT OF MECHANICAL ENGINEERING E.G.S.PILLAY ENGINEERING

COLLEGENAGAPATTINAN

N.ALBERT

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

Phases of DischargePhases of DischargeThe discharge process during EDM The discharge process during EDM can be separated into three main can be separated into three main phases phases 

•Preparation phasePreparation phase• Discharge phase Discharge phase •Interval phaseInterval phase

The effect of various input parameters The effect of various input parameters on material removal rate (MRR) and on material removal rate (MRR) and surface roughness (Ra) is discussed surface roughness (Ra) is discussed belowbelow

Pulse-on timePulse-on time Pulse-off timePulse-off time Flushing PressureFlushing Pressure Tool rotationTool rotation

The removal of material in electrical The removal of material in electrical discharge machining is based upon discharge machining is based upon the erosion effect of electric sparks the erosion effect of electric sparks occurring between two electrodesoccurring between two electrodes

1. Electro-mechanical theory1. Electro-mechanical theory2. Thermo-mechanical theory2. Thermo-mechanical theory3. Thermo-electric theory3. Thermo-electric theory

This theory suggests that abrasion of This theory suggests that abrasion of material particles takes place as a result material particles takes place as a result of the concentrated electric field.of the concentrated electric field.

The theory proposes that the electric field The theory proposes that the electric field separates the material particles of the separates the material particles of the work piece as it exceeds the forces of work piece as it exceeds the forces of cohesion in the lattice of the material. cohesion in the lattice of the material.

This theory neglects any thermal effects. This theory neglects any thermal effects.

This theory suggests that material removal This theory suggests that material removal in EDM operations is attributed to the in EDM operations is attributed to the melting of material caused by "flame jets".melting of material caused by "flame jets".

These so - called flame jets are formed as a These so - called flame jets are formed as a result of various electrical effects of the result of various electrical effects of the discharge. discharge.

However, this theory does not agree with However, this theory does not agree with experimental data and fails to give a experimental data and fails to give a reasonable explanation of the effect of reasonable explanation of the effect of spark erosion. spark erosion.

This theory, best-supported by This theory, best-supported by experimental evidence, suggests that metal experimental evidence, suggests that metal removal in EDM operations takes place as a removal in EDM operations takes place as a result of the generation of extremely high result of the generation of extremely high temperature generated by the high temperature generated by the high intensity of the discharge currentintensity of the discharge current

Although well supported, this theory cannot Although well supported, this theory cannot be considered as definite and complete be considered as definite and complete because of difficulties in interpretation.because of difficulties in interpretation.

The EDM setup consists of a power supply The EDM setup consists of a power supply whose one lead is connected to the work whose one lead is connected to the work piece immersed in a tank having dielectric piece immersed in a tank having dielectric oil.oil.

The tank is connected to a pump, oil The tank is connected to a pump, oil reservoir, and a filter system.reservoir, and a filter system.

The pump provides pressure for flushing The pump provides pressure for flushing the work area and moving the oil while the work area and moving the oil while the filter system removes and traps the the filter system removes and traps the debris in the oildebris in the oil

To flush the eroded particles produced To flush the eroded particles produced during machining, from the discharge during machining, from the discharge gap and remove the particles from the gap and remove the particles from the oil to pass through a filter system. oil to pass through a filter system.

To provide insulation in the gap To provide insulation in the gap between the electrode and the work between the electrode and the work piece. piece.

To cool the section that was heated by To cool the section that was heated by the discharge machining. the discharge machining.

Flash PointFlash Point Dielectric StrengthDielectric Strength ViscosityViscosity Specific GravitySpecific Gravity ColorColor OdorOdor

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

The work material chosen for this experimental work The work material chosen for this experimental work is is OHNS (Oil-Hardening Non-Shrinkable)OHNS (Oil-Hardening Non-Shrinkable) die die steelsteel which is one of the most widely used die steel which is one of the most widely used die steel material for the manufacture of press tools; cutting material for the manufacture of press tools; cutting dies and punches for blanking, trimming, flanging dies and punches for blanking, trimming, flanging and forming operations. and forming operations.

The important characteristics responsible for the The important characteristics responsible for the commercial popularity of this material are its ability commercial popularity of this material are its ability to retain accurate dimensions at elevated to retain accurate dimensions at elevated temperatures, abrasion resistance, toughness and temperatures, abrasion resistance, toughness and negligible deformation during the hardening process.negligible deformation during the hardening process.

It is commercially machined in the hardened state It is commercially machined in the hardened state with EDM process using copper as the electrode with EDM process using copper as the electrode material and kerosene as the dielectric medium. material and kerosene as the dielectric medium.

The chemical composition of this work material is The chemical composition of this work material is given in Table. No literature on the machining given in Table. No literature on the machining aspects of this material using any other electrode aspects of this material using any other electrode material or dielectric medium besides copper and material or dielectric medium besides copper and kerosene could be found.kerosene could be found.

The electrical discharge machine (model Electronica – M2S) with The electrical discharge machine (model Electronica – M2S) with Servo-head and positive polarity for the electrode was used to Servo-head and positive polarity for the electrode was used to conduct the experiments.conduct the experiments.

Commercial grade kerosene used as dielectrics and side Commercial grade kerosene used as dielectrics and side flushing with a pressure of 15 lbs/influshing with a pressure of 15 lbs/in22 was maintained for the was maintained for the whole experiment. The sparking voltage was fixed at 80 V and 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 was varied from 4A to 15 A. In all, values of discharge current, namely, 15A, 12A, 10A,6A were used for discharge current, namely, 15A, 12A, 10A,6A were used for Brass electrode material, and 10, 7A, 6A, 5A, 4A were used for Brass electrode material, and 10, 7A, 6A, 5A, 4A were used for Copper electrode material All the experiments were conducted Copper electrode material All the experiments were conducted with positive polarity of the electrode.with positive polarity of the electrode.

Besides discharge current, two other variables related to the Besides discharge current, two other variables related to the spark pulse wave are on time and off- time which can be set spark pulse wave are on time and off- time which can be set independently. The diameter of crater formed during each spark independently. The diameter of crater formed during each spark is proportional to the applied current while its depth is is proportional to the applied current while its depth is proportional to the on- time. proportional to the on- time.

Two electrodes were machined to a cylindrical Two electrodes were machined to a cylindrical shape of 14 mm diameter and 50mm lengthshape of 14 mm diameter and 50mm length

A plate of 200 mm ×60 mm size and thickness A plate of 200 mm ×60 mm size and thickness 18 mm of OHNS die steel was taken. It was 18 mm of OHNS die steel was taken. It was subjected to a standard hardening cycle and it subjected to a standard hardening cycle and it has a hardened at the range of 40 to 45 HRChas a hardened at the range of 40 to 45 HRC

After mounting the work piece and one of the After mounting the work piece and one of the electrodes on the machine, the depth of electrodes on the machine, the depth of machining was set at 25mmmachining was set at 25mm. .

Electrode material has a significant Electrode material has a significant influence on important output influence on important output parameters, such as, material removal parameters, such as, material removal rate, surface roughness and rate, surface roughness and dimensional accuracydimensional accuracy

Copper can be easily machined to any Copper can be easily machined to any shape, suffers less wear, has good shape, suffers less wear, has good thermal conductivity, and is thermal conductivity, and is economical.economical.

Brass is inexpensive and very easy to Brass is inexpensive and very easy to machine, but it has high electrode machine, but it has high electrode wear. wear.

PROPERTYPROPERTY UNITUNIT

MATERIALMATERIAL

COPPERCOPPER BRASSBRASS

Thermal conductivityThermal conductivity W/m-KW/m-K 391391 159159

Electrical resistivityElectrical resistivity Ohm-cmOhm-cm 1.671.67 4.74.7

Specific heat capacitySpecific heat capacity J/g-deg CJ/g-deg C 0.3850.385 0.380.38

Melting pointMelting point Deg CDeg C 10831083 990990

ELEMENTELEMENT COMPOSITION,wt%COMPOSITION,wt%

CarbonCarbon 09 to 1.009 to 1.0

SiliconSilicon 0.3 to 0.50.3 to 0.5

ManganeseManganese 0.7 to 0.80.7 to 0.8

ChromiumChromium 0.5 to 0.60.5 to 0.6

TungstenTungsten 0.5 to 0.60.5 to 0.6

VanadiumVanadium 1.01.0

IronIron BalanceBalance

Sparking Voltage (V)Sparking Voltage (V) V80±5%V80±5%

Discharge Current (A)Discharge Current (A) 15,12,10,8,7,6,5,415,12,10,8,7,6,5,4

Servo ControlServo Control Electro MechanicalElectro Mechanical

PolarityPolarity Normal (Electrode – PositiveNormal (Electrode – Positive

Dielectric fluidDielectric fluid Commercial Grade KeroseneCommercial Grade Kerosene

Flushing sideFlushing side Flushing with PressureFlushing with Pressure

Work piece MaterialWork piece MaterialOHNS Die Steel (Hardened and OHNS Die Steel (Hardened and

Tempered)Tempered)

Electrode MaterialElectrode Material Copper and BrassCopper and Brass