Title: INVESTIGATION%20IN%20ELECTRIC%20DISCHARGE%20MACHINING%20ON%20OHNS%20STEEL%20TO%20INCREASE%20THE%20SURFACE%20FINISH%20AND%20REDUCE%20THE%20HEAT%20AFFECTED%20ZONE%20BY%20VARIOUS%20MACHINING%20PARAMETERS
1INVESTIGATION IN ELECTRIC DISCHARGE MACHINING ON
OHNS STEEL TO INCREASE THE SURFACE FINISH AND
REDUCE THE HEAT AFFECTED ZONE BY VARIOUS
MACHINING PARAMETERS
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
2INVESTIGATION IN ELECTRIC DISCHARGE MACHINING ON
OHNS STEEL
N.ALBERT
3ELECTRIC DISCHARGE MACHINING
- 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
4SCHEMATIC OF AN ELECTRIC DISCHARGE MACHINING
(EDM) MACHINE TOOL
5EDM DISCHARGE PHENOMENA
- Phases of Discharge
- The discharge process during EDM can be separated
into three main phases - Preparation phase
- Discharge phase
- Interval phase
6EFFECT OF INPUT PARAMETERS
- 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
7 THEORIES OF MATERIAL REMOVAL
- The removal of material in electrical discharge
machining is based upon the erosion
effect of electric sparks occurring between two
electrodes -
- 1. Electro-mechanical theory2.
Thermo-mechanical theory3. Thermo-electric
theory
8ELECTRO-MECHANICAL 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.
9THERMO-MECHANICAL THEORY
- 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.
10THERMO-ELECTRIC THEORY
- 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.
11DIELECTRIC FLUID
- 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
12DIELECTRIC FLUID
13THE MAIN FUNCTIONS OF THE DIELECTRIC FLUID
- 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.
14PROPERTIES OF DIELECTRIC FLUID
- Flash Point
- Dielectric Strength
- Viscosity
- Specific Gravity
- Color
- Odor
15EDM PERFORMANCE MEASURES
- A signif?cant 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.
16WORK MATERIAL
- 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. - 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.
17(No Transcript)
18EXPERIMENTAL PROCEDURE
- 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/in2
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.
19EXPERIMENTAL SETUP
- 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.
20EXPERIMENTAL SETUP
21ELECTRODE MATERIALS
- 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.
22COMPARISON OF COPPER AND BRASS ELECTRODE
PROPERTY UNIT MATERIAL MATERIAL
PROPERTY UNIT COPPER BRASS
Thermal conductivity W/m-K 391 159
Electrical resistivity Ohm-cm 1.67 4.7
Specific heat capacity J/g-deg C 0.385 0.38
Melting point Deg C 1083 990
23 CHEMICAL COMPOSITIONS OF OHNS DIE STEEL
ELEMENT COMPOSITION,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 0.5 to 0.6
Vanadium 1.0
Iron Balance
24MACHINING PARAMETERS
Sparking Voltage (V) V805
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