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MACHINING CHARACTERISTICS OF A HYBRID PROCESS OF EDM IN GAS
COMBINED WITH ULTRASONIC VIBRATION AND AJM
SAJIN RLYANEME045
INTRODUCTION
In this paper the AJM and USV mechanisms were incorporated into the process of EDM in gas to develop a HYBRID EDM process.
ELECTRICAL DISCHARGE MACHINING (EDM)
Electrical Discharge Machining (EDM) is a non conventional machining process.
EDM machining method are used for hard metals which are electrically conductive.
The principle of EDM is spark erosion or electro erosion.
Uses a pulsating electric charge carrying high frequency DC current.
Generates a plasma channel between the two electrodes.
Dry EDM is a modification of the oil EDM process in
which the liquid dielectric is replaced.
Molten materials during EDM process was ejected from
machining zone by a high-speed air jet. .
Contd….
Kerosene used as the dielectric media in EDM process
induce some problems.
ABRASIVE JET MACHINING (AJM)
Abrasive jet machining (AJM) is process of material
removal by impact erosion.
A focused stream of abrasive particles 50 microns grit
size , carried by high pressure air or gas at velocity of 200
m/s is made to impinge on the work surface.
Aluminum oxide, Silicon carbide, and sodium
bicarbonate are some of abrasives used in AJM.
ULTRASONIC MACHINING (USM)
In Ultrasonic machining (USM), tool vibrates at an
ultrasonic frequency (19-25 kHz) with an
amplitude of around 5-50 μm over the workpiece.
Tool is pressed downward with a feed force.
As the tool vibrates over the workpiece, the
abrasive particles act as the indenters and indent
both the work material and the tool.
HYBRID EDM PROCESS
Develop a hybrid process integrating various mechanisms to improve the machining characteristics.
The effects of dielectric media and peek current in the hybrid EDM process were examined on the machining characteristics such as material removal rate (MRR), electrode were rate (EWR), and surface roughness (SR).
To find surface morphologies and thickness of recast layer of SKD 61 tool steel in hybrid process.
EXPERIMENTAL METHOD
A die-sinking EDM machine with transistor controlled
circuit integrated is used.
SKD 61 steel was selected as the workpiece material, which
dimension is Φ15 mm×5 mm.
The dielectric media were adjusted by a regulated pressure
valve to fit the requirement of experimental conditions.
Gas with specific abrasives was delivered through central
hole of electrode.
WORKING PROCESS
Melting and vaporizing material was ejected as fast
as possible by high-speed compressed gas jet.
USV and AJM were incorporated to facilitate the
materials removal efficiency.
Workpiece and electrode specimens were weighed
before and after each experiment to calculate the
MRR and EWR.
The SR was measured by a precision profilometer.
Scanning Electronic microscope (SEM) was used to
explore the integrities of machined surface
The dielectric media were used are air, oxygen, and
argon.
Input variables such as peak current (Ip), dielectric
media were varied to explore their influences on the
machining characteristics.
The machining time for each experiment is 10 min.
MATERIAL REMOVAL RATEImproved transport rate of debris and molten material.Preventing the secondary sparks .
EFFECTS OF THE HYBRID EDM PROCESS WITH VARIOUS DIELECTRIC MEDIA
RESULTS AND DISCUSSION
Higher EWR in hybrid EDM process than EDM in gas.AJM mechanism abrade the inner wall of the electrode
ELECTRODE WEAR RATEEl
ectr
ode
wea
r rat
e (m
g/m
in)
Dielectric media
AIR ARGONOXYGEN
Lower SR of hybrid EDM process. Hybrid EDM process reduce the asperities caused by USV and
AJM.
SURFACE ROUGHNESS
Peak current, Amp
Mat
eria
l rem
oval
rate
(mg/
min
)MRR enhanced with an increase of peak current.Oxygen: promote oxidation & sparking of EDM.
MATERIAL REMOVAL RATE
EFFECTS OF THE HYBRID EDM PROCESS WITH PEAK CURRENT
Oxygen Air Argon
Peak current, Amp
Elec
trod
e w
ear r
ate
(mg/
min
)EWR increases with the increasing of peak current.Highest EWR was gained by using oxygen.Argon has lowest EWR.
ELECTRODE WEAR RATE
Peak current, Amp
Surfa
ce ro
ughn
ess (
Ra/μ
m)
SR increased with peak current.
surface morphologies would be coarser & the SR was
larger as the peak current set at high levels.
SURFACE ROUGHNESS
EDM INCORPORATED WITH AJM (EDM+AJM) Morphology caused by EDM in gas combined AJM
illustrates obvious micro pores on the machined surface.
SURFACE INTEGRITY
HYBRID EDM PROCESS (EDM+AJM+USV)
Molten materials suffer from rapid cooling rate due to the high compressed dielectric media and the high frequency USV.
The surface tension stress exceeded the ultra-tensile strength. Thus, the micro cracks were easily formed.
Thickness of the recast layer obtained by the EDM in gas combined AJM is larger than that obtained by the developed hybrid EDM process.
EDM INCORPORATED WITH AJM (EDM+AJM)
RECAST LAYER
Hybrid EDM process incorporates the USV which would inhibit the molten material to be redeposited on the machined surface.
The recast layer is thinner.
HYBRID EDM PROCESS (EDM+AJM+USV)
CONCLUSION
The MRR and EWR obtained by hybrid EDM process was higher
than that by EDM in gas.
SR gained by the hybrid EDM process was lower than that by
EDM in gas.
The machining characteristics such as MRR, EWR, and SR
increased with an increase of peak current.
The oxygen dielectric media generated the highest MRR, EWR and
SR in hybrid EDM process.
The argon dielectric media produced the lowest MRR, EWR and
SR in hybrid EDM process.
EDM in gas combined AJM have micro pores on the machined
surface, and that from hybrid EDM process reveals micro cracks
on the machined surface.
Thickness of the recast layer obtained by the EDM in gas
incorporated with AJM is thicker than that obtained by the
developed hybrid EDM process.
REFERENCES Electro Physical and Chemical Machining[2016] –Yan Cherng, Jung
Chou Hungb. Machining characteristics of hybrid EDM with ultrasonic vibration
and assisted magnetic force[2014] – Chuang FP, Wang AC, Chow HM Electrical discharge machining in Gas[1997]-Kunieda M, Yoshida Abrasive micro-blasting to improve surface integrity of electrical
discharge machining[2005]-Qu J, Shih AJ, Scattergood RO, Luo J Machining performance on hybrid process of abrasive jet machining
and electrical discharge machining[2012]- Lin YC, Chen YF, Wang AC, Sei WL
An investigation of ultrasonic assisted electrical discharge machining in gas[2006]- Zhang QH, Du R, Zhang JH, Zhang QB