1. A
P R E S E N TAT I O N
O N
Role Of Melting
Temperature Of The Work
Piece Material In EDM
SUBMITTED TO:- SUBMITTED BY:-
DR. Rabesh Kr. Singh Garima Singh and Ruchi Sharma
MTA 1ST YEAR
2ND SEM
2. LIST OF CONTENT
• Main considerations of EDM PROCESS
• Role of MP of material
• Effect on process and approach
• Effect on product quality
• Effect on time and set up of process
• Effect on MRR
• Effect on HAZ
• Mechanism etc.
3. THE FOUR MAIN CONSIDERATIONS FOR
EFFECTIVE EDM
THE WORK METAL,
EDM PROCESS PRIORITY(Surface Finish , MRR)
ELECTRODE MATERIAL
AND MACHINE.
• In case of the work metal (material being machined),
elemental structure, melting temperature and
thermal conductivity will impact the efficiency of
work machined on the EDM.
4. ROLE OF MELTING TEMPERATURE IN
EDM
• It can create difficulties for the EDM operator
(work process will be complex).
• It will effect the process parameters and approach.
• Quality of product can be damaged or effected .
• The time limit for a process will vary with each
material choice.
• Generally 800⁰C to 2,000⁰C Melting
temperature(material) is used while working in
EDM.
5. EFFECT ON PROCESS
• Since EDM is a thermal process, the melting
temperature and thermal conductivity of the work
metal can create difficulties for the EDM operator as
high melting point will create operation challenges.
• Work metals such as copper and copper alloys have
low melting points and high thermal conductivity,
which is suitable for EDM.
• If the same EDM approach is used regardless of work
metal, the end results could be vastly different. So the
melting temperature of material effects the approach of
the process.
6. EFFECT ON PRODUCT QUALITY
• Other metals (tungsten and carbide) have higher
melting points and lower thermal conductivity, and
require a spark hot enough to bring them to their
melting points but not so hot as to destroy the
integrity of the material.
• Low and moderate melting points are preferred in this
process as high melting point will create rough surface
and can damage the product quality.
7. EFFECT ON TIME AND SET UP
• The work metal’s melting temperature and thermal
conductivity require the EDM operator to adjust on-
time, polarity, voltage and off-time parameters,
which differ from one work metal to another.
• Workpiece properties like melting temperature,
electrical and thermal conductivity etc. directly
influences the range of applications of various
newly developed machining processes.
• Melting Temperature is inversely proportional to time
taken.
8. EFFECT ON MRR
• MRR is influenced by the melting point of
the workpiece material.
• Copper, as an example, has a low melting point, but the
metal removal is still generally low. This is due to copper
being a good thermal conductor. This means heat is
dissipated too quickly and therefore interferes with
efficient metal removal. Tool steel, on the other hand,
has a higher melting point, but is not as good as
thermal conductor and therefore has better metal removal
rates than copper.
9. Because copper is a good thermal conductor the energy
dissipates in the work metal giving a really low metal
removal rate .Tool steel is a poor thermal conductor and
gives a much higher metal removal rate.
10. EFFECT ON MRR
• MRR against the effect of melting temperature.
11. A CLOSE VIEW OF THE EDM
PROCESS
• The first phase also called ignition phase,
represents lapse corresponding to the occurrence of
break-down of the high open circuit voltage(Vi),
applied across the working gap having fairly low
discharge voltage(Vg).
• The Second phase is the formation of a plasma
channel surrounded by a vapour bubble.
• The Third phase is the discharge phase, when high
energy and pressurized plasma channel sustains for a
period of time.
12. • The Last phase is the collapse of plasma channel caused by
turning off the electric energy which causes molten metal to
violently eject.
13. HEAT AFFECTED ZONE IN EDM
• Heat affected zone is the area of the base material, which has
it's properties altered by heat intensive machining in EDM.
• Heat from the arc formation and subsequent flushing of
molten material leaves behind un- melted material
that cools unevenly forming a
layer whose properties are altered .
14. • Microscopic study of the machined component reveals three
kinds of layers:
Recast layer
Heat Affected Zone
Converted layers
• The re-cast layer is extremely hard and brittle, the surface is
porous and may contain micro cracks.
• Such surface should be removed before
using these products.
• The layer next to the recast layer is the “Heat Affected Zone”
(HAZ, which is approximately 25nm thick).
15. MATERIAL REMOVAL MECHANISM
In EDM, for a particular machining condition,
several phenomena are involved, I.e. ,
Heat conduction and radiation
Phase changes
Electrical forces
Bubble formation and collapsing
Rapid solidification etc.
16. • The forces that may be of electric, hydrodynamic in
nature remove the melted pools.
• The material removal process by a single spark is
as follows;
1. An intense electric field develops in the gap between
electrode and workpiece.
2. There are some contaminants inside fluid which build a
high- conductivity bridge between the electrode and
work piece.
3. When the voltage increases, the bridge and dielectric
fluid between the electrode and workpiece get heated
up.
4. The dielectric is ionized to form spark channel (Plasma
channel ).
Material Removal Mechanism
17. 5. The temperature and pressure increases and
spark is generated.
6. Bubbles rapidly expand and explode
during sparking until the voltage is turned off.
6. Next the heating channel collapses and the dielectric
fluid enters into the gap in order to flush away the
molten metal particles.
7. The discharge in EDM occurs in liquid.
Material Removal Mechanism
18. THE MATERIAL REMOVAL RATE
DEPENDS ON FOLLOWING FACTORS:
• Peak amperage or intensity of the spark.
• Length of the ON time
• OFF time- which influences the speed and stability.
19. REFERENCES
1. S.M. Pandit and K.P. Rajurkar, “A stochastic approach to thermal modeling
applied to electro-discharge machining”, Trans. ASME, Journal of Heat
Transfer 105 (1983) 555–562.
2. W. Natsu, M. Shimoyamadaand M. Kunieda,” Study on expansion process of
EDM arc plasma”, JSME International Journal, Series C 49 (2) (2006) 600–
605.
3. Text Book by Groover, 2010 edition.
4. Study of Workpiece Thermal Profile in Electrical Discharge Machining
Process ,Rohit Rajendran Dr. Vendan S. P
5. Prediction of Material Removal Rate in Die-Sinking Electrical Discharge
Machining Nur Sheril Loke Binti Izwan, Zhujian Feng, Jigar Bimal Patel,
and Wayne Nguyen Hung. Article
6. Analysis of EDM Performance, through a Thermal–Electrical Model with a
Trunk-Conical Discharge Channel, Using a Steel Tool and an Aluminium
Workpiece José A. S. Almacinha , Alice M. G. Fernandes †, Duarte A. Maciel
, Ricardo J. M. Seca .
