© 2020 ijrar june 2020, volume 7, issue 2 (e

© 2020 IJRAR June 2020, Volume 7, Issue 2 www.ijrar.org (E-ISSN 2348-1269, P- ISSN 2349-5138)

IJRAR2002368 International Journal of Research and Analytical Reviews (IJRAR) www.ijrar.org 845

ALUMINA NANO POWDER MIXED ELECTRIC

SPARK MACHINING OF AISI D3 DIE STEEL

Abstract

The growing trend to use slim, light and compact mechanical components in automobile, aerospace,

medical, missile, and nuclear reactor industries has led to the development of high strength, temperature resistant,

and hard materials during last few decades. It is almost impossible to find sufficiently strong and hard tools to

machine aforesaid materials at economic cutting speeds

The aim of this project to surface integrity of machined surface of AISI D3 Die steel by impregnating the

powder particles of Al2O3 in EDM oil used as a dielectric during Electro Sparking Machining (ESM). This

method of introducing nanoparticles in the dielectric fluid is known as powder mixed ESM (PMESM). An

experimental setup was developed and the experiments were conducted by varying four different parameters

such as powder concentration, peak current, pulse-on time, and gap voltage according to the central composite

design (CCD) of response surface methodology (RSM). Effects of these parameters along with powder

concentration were investigated on various EDM characteristics such as material removal rate (MRR), surface

roughness (SR). Results are clearly indicated that addition of powder to dielectric has significantly improve the

MRR and surface integrity.

Key words: Powder mixed EDM; AISI D3 Die steel; Material removal rate; Surface Roughness; RSM

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Chapter 1 INTRODUCTION

1.1. Introduction

The mechanical components used in different fields such as automobile, aerospace, medical etc., has

led to the development of high strength, temperature resistant, and hard materials during last few decades. It is

almost difficult to find sufficiently strong and hard tools to machine aforesaid materials at economic cutting

speeds. To meet the challenges, non-conventional machining processes are being employed to achieve higher

metal removal rate, better surface finish with less tool wear. Among all available non- conventional machining

methods Electric Spark Machining (ESM), otherwise called Electric Discharge Machining (EDM) is mostly used

for machining hard materials which are difficult to machine by conventional machining process. There are

various types of products which can be produced using ESM with high precision and good surface quality, such

as dies, moulds, parts for aerospace, automobiles, etc. In the ESM process thermal energy generated due to

series of sparks between tool and work piece is used to erode the work piece. The work piece which is

electrically conductive material is submerged into the dielectric fluid for better erosion [1].

Accumulation of debris in gap space in ESM which causes inactive pulses such as short and open circuit

and arc. These types of discharges do not remove any material from the workpiece and damage the surface

integrity of machined specimen. In order to overcome this challenge researchers in the past decade developed

several methods namely (1) Electrode rotation [2], (2) Electrode orbiting- planetary motion to either tool or

work piece [3], (3) Providing ultrasonic vibration to tool [4-6] and (4) Suspension of powder into dielectric

fluid [7]. Among these, introducing conductive particles in the dielectric fluid is a recent development1.This

method of introducing conductive particles in the dielectric fluid is known as powder mixed ESM (PMESM).

The conductive powder particles in the dielectric fluid increases the gap between the Tool and the workpiece

while providing a bridging effect between the electrodes for an even distribution of spark energy making the

process more stable.

Principles of ESM

Electro Spark Machining (ESM) is a type of thermo-electric process. In ESM process there is spark

generated between the work piece and tool electrode. In ESM process, between work piece and tool electrode

can’t be physically contacted. So for this spark generation both work piece and tool electrode should be

electrically conductive. For the ESM process electrode is the cutting tool and its cuts the work piece or




specimen with the shape of the present electrode. For connecting work piece and tool suitable power supply is

required. There is a small gap which is present between the tool and work piece and the work piece is submerged

in a dielectric fluid.

As the tool (electrode) is charged up by the supply and it brings near to the work piece. By this process

two conductors come near enough, due to which spark generation takes place between the tool and work piece

and due to this the removal of material from work piece is done. The process is continued until the shape of

electrode is formed in to work piece due to spark erosion. The basic parts of Electric Spark Machine are, work

piece, electrodes, power supply, dielectric fluid and servomechanism.

There are various kind of tool (electrodes) are used like as, brass, copper, tungsten etc. There are many

work pieces are used for the present time research work are like Die steel Stainless Steel, Inconel, carbide

Kerosene, etc. dielectric fluid in ESM is generally used EDM oil. Between the electrode and the work piece to

prevent them from contact each other a servomechanism is used and it maintains a space of about the thickness

of a human hair

Electrical Spark Machining (ESM) is a controlled metal-removal process that is used to remove metal by

means of electric spark erosion. In this process an electric spark is used as the cutting tool to cut (erode) the

work piece to produce the finished part to the desired shape. The metal-removal process is performed by

applying a pulsating (ON/OFF) electrical charge of high-frequency current through the electrode to the work

piece. This removes (erodes) very tiny pieces of metal from the work piece at a controlled rate. ESM spark

erosion is the same as having an electrical short that burns a small hole in a piece of metal it contacts. A pre-

shaped or formed electrode (tool) is shaped to the form of the cavity it is to reproduce. The formed electrode is

fed vertically down and the reverse shape of the electrode is erodes (burned) into the solid work piece.

Fig.1.1 Schematic diagram of ESM




PMESM Mechanism

The electro-sparking method of metal working involves an electric erosion effect which connotes the

breakdown of electrode material accompanying any form of electrics park i.e Fig 1.2 shows ESM process. A

necessary condition for producing a discharge is the ionization of the dielectric, that is, spilitting up of its

molecules into ions and electrons. Consider the case of a spark between two electrodes (tool cathode and work

anode) through a gaseous or liquid medium. As soon as suitable voltage is applied across the electrodes, the

potential intensity of the electric field between them builds up, until at some predetermined value, the individual

electrons break loose from the surface of the cathode and are impelled towards the anode under the influence

of field forces. While moving in the inter-electrode space, the electrons collide with the neutral molecules at the

dielectric, detaching electrons from them and causing ionization. At some time or the other, the ionization

becomes such that a narrow channel of continuous conductivity is formed. When this happens, there is a

considerable flow of electrons along the channel to the anode, resulting in a momentary current impulse or

spark. The liberation of energy accompanying the discharge leads to the generation of extremely high

temperature, between 8000⁰c and 12000⁰c causing fusion or partial vapourization of the metal and the dielectric

fluid at the point of discharge. The metal in the form of liquid drops is dispersed into space surrounding the

electrodes by the explosive pressure of the gaseous products in the discharge. This results in the formation of a

tiny crater at the point of discharge in the work piece [8].

Fig 1.2 Series discharging in PMESM

Process variables

Discharge current or peak current (Ip):

During each pulse-on time, current rises until it attains a certain predetermined level that is termed as

discharge current or peak current. It is governed by the surface area of cut. Higher currents produce high MRR,

but at the cost of surface finish and tool wear. Accuracy of the machining also depends on peak current, as it

directly influences the tool wear.




Discharge voltage (V):

Open circuit voltage between the two electrodes builds up before any current starts flowing between

them. Once the current flow starts through plasma channel, open circuit voltage drops and stabilizes the

electrode gap. A preset voltage determines the working gap between the two electrodes. It is a vital factor that

influences the spark energy, which is responsible for the higher MRR, higher tool wear rate and rough surfaces.

Pulse-on time or pulse duration (Ton):

It is the duration of time (µs), the current is allowed to flow per cycle. Dielectric ionizes and sparking

takes place during this period. It is the productive regime of the spark cycle during which current flows and

machining is performed. The amount of material removal is directly proportional to the amount of energy

applied during this on-time. Though MRR increases with Ton, rough surfaces are produced due to high spark

energy.

Pulse-off time or pulse interval (Toff ):

It is the duration of time between two consecutive pulse-on times. The supply voltage is cut off during

pulse-off time. Dielectric de-ionizes and regains its strength in this period. This time allows the molten material

to solidify and to be washed out of the arc gap. Pulse-off time should be minimized as no machining takes place

during this period. However, too short Toff leads to process instability.

Duty cycle (τ):

It is a percentage of the on-time relative to the total cycle time. This parameter is calculated by dividing

the on-time by the total cycle time (on-time and off-time). At higher, the spark energy is supplied for longer

duration of the pulse period resulting in higher machining efficiency.

Electrode Polarity:

Straight polarity work piece is +Ve and Reversed polarity work piece is – Ve. It has dramatic effect.

Electrode with +Ve polarity wear less. Electrode with – Ve polarity cut faster. Some metal do not respond this

way. Carbide, Titanium, Copper generally cut with – Ve polarity Hard alloys steels cut by normal polarity.

Categories of ESM

ESM facilitates the machining in a number of ways, a lot of these operations are

similar to conventional machining operation, for instance milling and die sinking. A variety of classifications




are possible and recent developments in its technology append new operations owing to increase in various

requirements. A simple and general classification can be given in view of standard applications such as,

1. Die sinking ESM

2. Electric discharge milling (ED milling)

3. Electric discharge grinding (EDG)

4. Wire EDM (WEDM)

5. Micro-EDM (μ-EDM)

Die sinking ESM

Die sinking ESM, comprises a tool electrode and workpiece that are immersed in an insulating dielectric

fluid. A pulsating power supply that produces a voltage potential, connects the tool and workpiece. A constant

gap between the tool and the workpiece is maintained by a servo motor control of the tool holder. As tool move

towards the workpiece, dielectric breaks down into electrons and ions, creating a plasma column between two

electrodes. A momentary flash jumps between the electrodes. Automatic movement of tool, towards

workpiece takes place as the spark gap increases due to metal erosion. Thus the process continues without

any interruption. As a result, the complementary shape of the tool electrode accurately sinks into the workpiece.

Electric spark milling

Electric spark (ES) milling is an evolution of CNC contouring ESM. A rotating cylindrical

electrode follows a programmed path in order to obtain the desired shape of a part, like a cutter

used in conventional computerized numerical controlled (CNC) milling. Compared to traditional sinking

ESM, the use of simple electrodes in ES milling eliminates the need for customized electrodes. In the ES

milling, the simple shape electrode does layer-by-layer milling to get a three-dimensional complex parts, at the

same time, electrical sparks occur repeatedly to remove materials along the programmed path. According to the

spark status between the electrode and the workpiece, the control system determines the forward and withdrawal

feed rate of the electrode [3].

Electric spark grinding

Electric spark grinding (ESG) is the process which works on the same principle as

ESM. A rotating wheel made of electrically conductive material, is used as a tool. A part of the

grinding wheel (cathode) and workpiece (anode) both are immersed in the dielectric,




and are connected to DC power supply. The rotating motion of the wheel ensures effective flow of

dielectric in the IEG, and hence flushing the gap with dielectric can be eliminated. Mechanism of material

removal is exactly same as in ESM except that rotary motion of the tool helps in effective ejection of the molten

material. Contrary to conventional grinding, there is no direct physical contact between the tool and workpiece,

hence fragile and thin sectioned specimens can be easily machined. ESG is also considered to be economical

compared to the conventional diamond grinding [1].

Wire ESM

Wire ESM uses a very thin wire of 0.02 to 0.03 mm diameter usually made of brass or stratified copper

as electrode and machines the workpiece with electric discharges by moving either the wire or workpiece.

Erosion of workpiece by utilizing spark discharges is very same as die sinking ESM. The predominant feature

of a moving wire is that a complicated cut can be easily machined without using a forming tool. This process

is frequently used to machine plates about 300 mm to manufacture dies, punches, and tools from hard materials

which are difficult to machine using other processes.

Micro-ESM

The present trend of miniaturization of mechanical parts has given µ-ESM a considerable research

attention. Using this process, it is possible to produce shafts and microholes diameter as less as 5 µm,

and also intricate three-dimensional shapes [6]. It is extensively utilized for the fabrication of micro arrays,

tool inserts for micro-injection molding, and hot embossing. In the beginning,µ-ESM was employed

mostly for fabricating small holes in metal sheets. Owing to the versatility of the process, currently it is used in

the manufacturing of micro molds and dies, tool inserts, micro filters, micro fluidic devices, housings for micro-

engines, surgical equipment etc.

Applications

ESM has been used in manufacturing of aerospace components such as fuel system, engine, impeller and

landing gear components where high temperature and high-stress conditions prevail. However, the safety and

life of the components were questionable due to poor surface integrity. Application of PMESM process in place

of conventional ESM adequately addressed the problem arising due to poor surface integrity. Some of the

specific applications of PMESM in automobile industry include the manufacturing of engine blocks, cylinder

liners, piston heads and carburetors. With the increased precision, accuracy and the capability to be used under

micro machining domain, PMESM is also used to produce medical implants and surgical equipment. Some of

the specific devices include surgical blades, dental instruments, orthopedic, spinal, ear, nose, and throat

implants. Surface modification in the form of electro discharge coating is also realized by

PMESM technique. Therefore, light metallic alloys can be surface treated for wear resistance applications




typically in automobile and aerospace industries.




Chapter 2 Literature survey




Introduction

In PMESM, the addition of suitable powder particles to the dielectric leads to a superior surface finish,

and better machining rate compared to those for conventional ESM (without powder-mixed dielectric). A novel

ESM two-tank system was first developed and marketed by Mitsubishi [9]. One of the tanksconsisted of

standard dielectric oil and the second one contained powder-mixed dielectric. After completion of initial

machining operation in the first tank, the tool head moved to the second tank to perform the finish machining.

However, the extensive application of PMESM in the industry requires a thorough understanding of its

mechanism and the influence of different powder characteristics on performance measures.

Density, size, electrical and thermal conductivities are some of the critical characteristics

of the powder particles that significantly affect PMESM process. Increase in electrical

conductivity of the dielectric, and resulting extension of spark gap in PMESM, as

discussed earlier, enhance spark frequency and facilitate easy removal of debris from the machining

zone [10].

High thermal conductivity of powder particles removes a large amount of heat from the discharge gap

leading to reduction in discharge density. Therefore, only shallow craters are formed on the workpiece surface

[11]. Number of surface cracks developed on the machined surface are also reduced along withtheir width and

depth, as the intensity of discharge energy is less in PMESM compared to conventional ESM process [12, 13].

Table 2.1 Properties of various powder materials

Material Density

(g/cm3)

Thermal

conductivity

Reference

Graphite (C) 1.26 3000 [14-15]

Carbon nanotubes (CNTs) 2.00 4000 [16-19]

Silicon (Si) 2.33 168 [20]

Boron Carbide (B4C) 2.52 27.9 [21]

Aluminum (Al) 2.70 237 [22-24]

Alumina (Al2O3) 3.98 25.1 [25]

Variants of EDM

The capability to machine virtually any electrically conductive material, the applications of electric

Spark machining (ESM) are restricted to a few industries, due to poor productivity and surface quality of the




machined components. Over the years, researchers have developed new variants to ESM for enhancing its

performance. Some of them include the rotation of tool, ultrasonic vibration of the tool/workpiece/dielectric,

and utilization of powder-mixed dielectric.

Rotation of tool

Rotary motion is given to tool electrode, in the normal direction to the workpiece surface.

Centrifugal force induced through rotary motion, drags the dielectric in to the inter electrode gap, enabling

easier debris removal. Other advantages of the technique over stationary electrode include reduced tendency of

arcing and improved sparking efficiency which finally lead to higher MRR, diminished too wear and surface

roughness.

Ultrasonic vibration of tool/workpiece

The higher efficiency gained by the employment of ultrasonic vibration is mainly attributed

to the improvement in dielectric circulation which facilitates the debris removal and the creation of a

large pressure variation between the electrode and the work piece, as an enhancement of molten metal

ejection from the surface of the workpiece. Zhang et al. proposed spark erosion with ultrasonic

frequency using a DC power supply instead of the usual pulse power supply. The pulse

discharge is produced by the relative motion between the tool and work piece simplifying the

equipment and reducing its cost. They have indicated that it is easy to produce a combined technology

which benefits from the virtues of ultrasonic machining and ESM. Vibro-rotary motion (combination of

vibration and rotation) of tool produces superior MRR compared to simple vibration or rotation alone.

Moreover, use of ultrasonic vibration under micro-ESM regime has also been found to be quite productive.

When vibration is imparted in the workpiece there is an improvement in flushing efficiency. Additionally

increase in amplitude and frequency during ultrasonic vibration assisted micro-ESM enhances MRR.

Influence of machining parameters

The combined and individual characteristics of dielectric, powder, tool and workpiece material along

with other machining parameters affect the PMESM process significantly [26]. The effect of important process

parameters on the machining characteristics of PMESM process is discussed below.

Dielectric

Apart from commercial EDM oils, kerosene, and deionized water are widely used in PMEDM. The

higher thermal conductivity and specific heat of pure water take away the heat from the machining zone

resulting in a better cooling effect [27].




Simultaneously, kerosene forms carbides and water forms oxides on the machined surface.Carbides require

more thermal energy to melt compared to oxides [28]. This was attributed to the increase in overall electrical

conductivity of the dielectric due to the ionization of water soluble anionic compound emulsifier present in the

emulsified oil.

Literature survey

F.Q.Hua et al [29] conducted experiments on surface properties of SiCp/Al with moderate friction of SiC

particle reinforced Al matrix composites in EDM and PMEDM using Environment scanning electron

microscope. They have found that the surface properties are improved greatly in PMEDM than EDM as its

surface roughness decreased about 31.5% and is better in corrosion resistance and wear resistance is twice of

EDM. Finally they have also mentioned that the PMEDM is having Promising applications in metal matrix

composites machining field.

M Prabu et al [30] have done done experimental investigation on effect of graphite powder suspended

dielectric in electric in EDM of Al-TiB2 composites. The experiments were conducted on ELEKTRAPULS

spark erosion machine. Their objective is to find the effect of parameters viz, current, pulse ON-time, flushing

pressure and vibration. As a result, the process becomes more stable thereby improving Material Removal Rate

(MRR) and reducing Tool Wear Rate (TWR). The EDM setup is used in their experimental study is M100

model die sinking EDM machine manufactured by Electronica Machine Tools. The Parameters and their

settings are in L16 orthogonal array. It uses Kerosene as the dielectric fluid. The primary benefit of using

kerosene is that it has very low viscosity and gets flushed away easily. The selected work piece material is Al-

TiB2 composites. Each experiment was performed for fixed time period using brass as an electrode. Input

process parameters are current, pulse on time and flushing pressure. The material removal rate and tool wear are

evaluated by using an electronic balance machine. They have conducted that this work evaluates the feasibility

of machining Al-TiB2MMC with graphite powder suspended dielectric fluid. MRR was found higher for larger

current. When comparing the MRR of with powder and without powder the MRR obtained for with powder is

found higher. TWR slightly increases with increasing the current. When comparing the TWR of with powder

and without powder the TWR obtained for with powder is found higher. Increase in MRR was found on

increasing Pulse ON-time. TWR increases with the increases in pulse ON-time.

B Govindharajan et al [31] focused on performance of nickel mixed with kerosene as dielectric medium in

electrical discharge machining of Monel 400TM. The optimum range of nickel powder, Graphite powder 6g

mixes with the dielectric medium of kerosene servotherm (75:25) were developed experimentally. It was




reported slightly more removal rate, very low tool wear rate, better dimensional accuracy and good surface

finish in Monel 400TM. They have concluded that the experimentally observed performance of kerosene-

Servotherm of different proportion of nickel powder found that better machining output in EDM of Monel

400TM. The surface smoothness and diameteral accuracy reported by kerosene servotherm of 8g nickel mixed

dielectric medium gives better result. After than drawn all graphs which shows the optimum proportion mixture

of nickel powder influences the MRR, TWR and OC.8, 6g of nickel and graphite powders are mixed with

kerosene-servotherm (75:25) gives better results of MRR, TWR and OC.

R.A.prajapati et al (2015) [32] experimented on SiO2 powder mixing into a dielectric fluid of EDM on

machining characteristics of EN-8. Three input parameters are involved in this study namely peak current,

pulse-on time and concentration of powder. En-8 is used as a work piece, copper is used as an electrode,

kerosene as a dielectric with the presence of SiO2 in EDM. The analysis was carried out for surface roughness

which gives better experimental results with zero concentration of rather than PMEDM. Based on literature

survey for better surface finish can be obtained at peak current (9A), powder concentration(0g/l), pulse-on

time(25µm).

SatpalKundu, Surender Kumar, Ravinder Chaudhary et al.(2014) [33] carried out a study of MRR on H13

die tool steel by using EDM and Taguchi technique is used. With this procedure results are obtained as follows:

when pulse-on time and current increases, MRR increases and when increase in feed rate value, MRR decreases.

C. MathalaiSundaram, R. Siva Subramanian et al.(2013) [34]carried out a study of on machining process

parameters of EDM on aluminium and copper as a tool electrode, OHNS steel used as a work piece which is

non-shrinking die steel and oil hardening. From this investigation observed that current increases MRR and

EWR increases.

Kamajit Singh, C S Kalra et al.(2013) [35]OHNS die steel is used for EDM process in input parameters were

choosen as peak current, pulse-on time, voltage gap and flushing pressure. Taguchi and ANOVA methods are

used in this process for optimization. The results are observed that large effect current on MRR and large effect

of flushing pressure on hardness of die steel.

H.K.Kansa, Sehijpal Singh, Pradeep Kumar et al.(2007) [36] study on effect on silicon powder mixed in

kerosene as a dielectric fluid in EDM. Copper (25 dia) as a tool electrode, AISI D2 die steel as a work piece

which is used in EDM. There are six parameters namely peak current (16A), pulse-on time (100µs), pulse- off

time (15µs), concentration of powder (4 g/l), gain (0.83 mm/s) and nozzle flushing. Taguchi method is used for

optimization, ANOVA is used for peak current and powder concentration towards MR is maximum.




Reza, M.S, Azmir et al (2011) [37] effect of machine polarity of AISI P20 GRADE 1.2738 alloy steel using a

copper electrode by DOE using L18 orthogonal array. The positive polarity gives TWR, MRR and SR with

optimal results.

Shivam Goyal, Rakesh Kumar Singh (2014) [38] has been studied effect of aluminum powder mixed with

EDM oil influencing on the surface finish and MRR. AISI 1045 act as an work piece and copper act as an

electrode in EDM machining. The result of this study, with increasing concentration of aluminum powder and

grain size, MRR and SR decreases.

M.A Razak, A.M.Abdul Rani and A.M. Nanimina (2014) [39] has been studied effect on silicon powder

using graphite and copper electrode, stavax as a work piece which influences the PMEDM machining. Seven

experiments are conducted based on taguchi orthogonal array with three level and two factors. The parameters

are used in the study are powder concentration and grain size of powder. They found the results of the study,

increase of MRR, improve SF, reduce TWR, reduce machining time and cost.

Chow et al (2008) [40] proposed the use of SiC powder having a size of 3µm -5µm is mixed in water which act

as a dielectric in EDM machining of titanium alloys and addition of SiC powder enlarge the gap of electrode

and work piece, therefore MRR increases

Wong et al. (1998) [41] studied the mirror finish phenomenon in EDM, using Al powder at concentration 2 g/l

in dielectric fluid which influences the SKH-51 work piece.

.Abhishek Abrol et al (2015) [42] studied the effect of chromium powder dielectric fluid on machining of AISI

D2 die steel has been studied. The process parameters are pulse-on time, pulse-off time, peak current,

concentration of powder. The performance is measured in terms of MRR, TWR, SR. the experiment was

undertaken using a taguchi method. With the increase in current, TWR increases and with the increase in pulse-

off time, SR increases. With the increase in current and pulse-on time, MRR increases. It is also observed that

concentration of chromium powder increases, MRR and TWR decreases.

KuldeepOjha et al (2011) [43] have studied effect of chromium powder added into dielectric fluid of EDM

were chosen as a process parameter to study the powder mixed electrical discharge machining of EN-8 steel in

terms of MRR and TWR. The method used to analyse the experiments is response surface methodology (RSM).

Tan et al.(2008) [44] investigated the Effect of nanopowder additives on SR. SR decreases on usage of

Al2O3 and Silicon carbide nanopowders during the micro-EDM of stainless steel.

W.S. Zhao et al (2002) [45] have studied to improve the surface roughness and rough machining. EDM

machining has divided into two methods: rough machining and surface machining. Surface finishing requires

high surface quality, and roughness machining requires high machining efficiency which is obtained from




PMEDM.




2.4 Motivation and objective of research work

From the review of past research work, it is evident that PMEDM has strong potential in enhancing

MRR and surface finish. However, the criteria for powder material selection, based on specific requirements

and application, are still unknown. Therefore, it is essential to comparatively evaluate the performance of some

of the commercially available powders and correlate the same with different properties of these powder

materials. Moreover, previous studies primarily focused on MRR and surface finish in PMESM. Existing works

also reveal that the process parameters such as powder concentration, peak current, pulse-on time and gap

voltage have significant influence on ESM characteristics. While these performance measures undoubtedly

have enormous significance, surface integrity of the machined components perhaps plays a more vital role in

influencing the performance during their intended applications and deciding the service life of the same

components. Therefore, investigation into influences of various PMESM parameters on various aspects of

surface integrity is of utmost relevance. However, such studies have rarely been reported so far. It is also

observed from the literature that various methodologies were adopted to analyze different response

characteristics in PMESM. However, very few attempts have been made to correlate the interaction effect of

PMESM process parameters with process performance. A great deal of research work pertaining to PMESM of

different grades of steel has been published during the last decade or so. Cold-work tool steels which include

D2, D3, D4, D5, and D7 steels are high-carbon, high-chromium steels. Apart from D3 steel all group D steels

have 1% Mo and are air hardened. Type D3 steel is oil-quenched; though small sections can be gas quenched

after austenitization using vacuum. As a result, tools made with type D3 steel tend to be brittle during hardening.

Because the material is so tightly held and controlled in this setup, part flatness remains very true, distortion is

nearly eliminated, and edge burr is minimal. HCHCR D3 is used in cold Dies & tooling application that required

the achievement of high degree of accuracy in hardening & tempering, such as dies drawing, forming cold rolls,

powder metal tooling and blanking and trimming dies, blanking dies for paper and plastics, shear blades, cold

die punches, Ejector pins etc. Normally HCHCR D3 consists carbon of 2% and Chromium of 12% Silicon and

Manganese vary between 0.2-0.35% This is a direct hardening material and can be hardened to 58-60 HRC.

This material is used for manufacturing press tools and sheering blades.




Chapter 3

Problem definition and Applications




Problem definition

1. To determine and enclosure alumina Nano fluids with different volume concentrations.

2. To conduct the experiments on alumina nano fluids and EDM oil with and without surfactant.

3. To prepare the Nano fluids with different volume concentration of Nano particles.

4. To calculate the thermal conductivity, viscosity of alumina nano fluids and EDM oil.

5. To calculate the MRR, TWR, and Surface Roughness of alumina nano fluids with weights of (0g/l,

0.2g/l, 0.4g/l, 0.6g/l, 0.8g/l).

Advantages and Disadvantages of Nano fluids.

Advantages:

1. Enhance heat transfer rate greater than the conventional fluid.

2. Possess thermal conductivity of greater magnitudes than base fluids like water, ethylene glycol

etc.

3. Though the method is economic, the problem of storage, drying and transportation exists.

Disadvantages:

1. Sonication must be done at regular intervals in order to avoid settling down of nano particles.

2. Costlier when compared to conventional fluids.

3. Copper compounds may be irritating to eyes, skin and respiratory tract.




Chapter 4

Characterization of 𝐀𝐀𝐀𝐀𝐀 –EDM oil Nano fluids




Characterization of nano fluids

In the present study characterization was done for Al2O3- EDM oil nanofluids to know the behavior of

these fluids when used in EDM applications. Preparation of nano fluids can be done by two techniques 1. Single

step technique and 2. Two step techniques. Firstly, single step technique is a process of combining the

preparation of nano particles with the synthesis of nano fluids, for which the nano particles are directly prepared

by physical vapor deposition (PVD) technique or liquid chemical method. TiO2 – water nano fluids can be

dispersed by single step chemical method using a high pressure homogenizer [46]. In two step technique nano

particles dispersed into base fluids with various techniques like stirrer, ultra-sonication bath, an ultrasonic

disrupter to disperse nano fluids into the base fluids. They observed that two step technique works better for

oxide particles than the single step technique. The dis-advantage of two step technique is agglomeration of nano

particles occurs due to Van der waals forces. Nano fluids containing oxide particles and carbon nano tubes are

produced by this method. Oxide Nano particles is attractive for industry due to its simple preparing method

[47].

As-received Al2O3 powders were characterized using X-ray Diffraction equipment to determine the

actual size. X-ray diffraction (XRD) spectra of as-received powder is demonstrated in Fig 3.2. The crystallite

size of the SiC nanoparticles was determined by the X-ray line broadening method using the Scherer equation

[48]

k D =

cos(4.1)

Where D is the crystallite size in nanometers, λ is the wavelength of the radiation, k is a constant equal to 0.9,

β is the peak width at half maximum intensity, and θ is the peak position as shown in the Fig 4.1.

Fig 4.1 Photographic view of Al2O3 nano powder




Fig 4.2 X-Ray diffraction of Al2O3 nano powder

Physical properties of 𝐀𝐀𝐀𝐀𝐀 nano particles

The material of nanoparticles is chosen as Al2O3 because it is chemically more stable and its cost is

less than their metallic counterparts and also it is easily available.

Table 4.1 properties of 𝐀𝐀2𝐀3 nano particles

Property Value

Atomic weight 101.96 g 𝐀𝐀𝐀−1

Average particle size 50nm

Melting point 2055°C

purity 99.99%

Density 3.97 g/𝐀𝐀3

Color White

Morphology Spherical

Nano fluid stabilization

Stabilizing nano fluid depends upon colloidal system and attractive force existing between the particles.

The repulsive force must be larger compared to attractive force between the particles upon the ionic

concentration near the particles. It can be changed by steric stabilization used by many researchers to stabilize

nano fluids.

In steric stabilization with two different types of surfactant were carried out namely, Oleic acid and span

20 were chosen to be prepared in 0.004% volume concentration EDM oil – alumina nano fluids to stabilize and

it was carried out using ultra sonicator disrupter with a power of 100W. Different volume concentration has

been taken (0.004%, 0.008%, 0.011%, 0.015%) surfactant is added to stabilize and worked out in a Ultra

sonicator with a time of each 1 hour. Referred from Fig 4.2 and Fig 4.3 with different surfactant.




SPAN 20 has more stabilizing agent than compared to oleic acid because its HLB (hydrophilic- lipophilic

balance) value is 8.6 and oleic acid having 17.20. HLB value for a given surfactant is relative degree to which

the surfactant is water soluble or oil soluble. The lower HLB value the more lipophilic. The higher HLB value

the more hydrophilic.

Activator adding

Surfactant selection in nano fluids preparation has an important role in improving heat transfer.

Optimum percentage of surfactant should be considered as a factor in stable nano fluid preparation as well.

Addition of surfactant can improve the stability of nano particles in aqueous suspensions. Care should be taken

to apply enough surfactant as inadequate surfactant cannot make a sufficient coating that will persuade electro

static repulsion and compensate the van der waals attraction [49]. Popular surfactants have been used in

literature can be listed as sodium dodecylsulfate (SDS) [50], Gum Arabic, Oleic acid [51].

Fig 4.3 EDM oil– alumina nano fluid with span 20 after 1 hour ultra-sonication, no color change.

Fig 4.4. EDM oil- alumina nano fluid with oleic acid after 1 hour ultrasonication, no color change




Preparation of Nano fluids

The Al2O3 nano particles having an average size of 50nm and density of 3.97g/cm3. Preparing the Nano

fluids with desired concentration and dispersed equivalently into EDM oil and care should be taken to complete

dispersion. After weighing the Nano particles of Al2O3 (0.02, 0.04, 0.06, 0.08) grams were mixed in 250ml

flask for testing whether it is dispersing by using ultra sonication or magnetic stirrer. In sonication it depends

upon time of 3-4 hrs sedimentation will not observed for the range of concentration.

Table 4.2 various Properties of powder material

Material Density (g/cc) Electrical

Resistivity (µΩ-cm)

Thermal conductivity

(W/mK)

Chromium (Cr) 7.16 2.6 95

Silicon (Si) 2.33 2325 168

Tungsten (W) 19.25 5.3 182

Aluminum (Al) 2.7 2.89 236

Alumina (Al2O3)

3.98 103 25.5

Mixing of 𝐀𝐀𝐀𝐀𝐀nano powder in the EDM oil

Nano particles directly mixed in the base fluid and thoroughly stirred with magnetic stirrer or ultra-

sonicatior. Nano fluid prepared in this method give poor suspension stability, nano particles settle down due to

the gravity, after a few minutes of nanofluid preparation. The particle settlement depends on the type of nano

particles used, density and viscosity properties of the host fluids.

By adding surfactant to the 𝐀𝐀𝐀𝐀𝐀 nanofluid

In this method small amount of suitable surfactant in one-tenth of nano particles is added to the base

fluid and stirred continuously for 1hour. By adding the surfactant in nano fluids will give a stable suspension

with uniform particles dispersion in the host liquid. The nano particles remains in suspension state for a long

time without settling down at the bottom of the container. To avoid sedimentation, SPAN 20 is used as

surfactant for the current investigation. SPAN 20 HLB value is 8.6. In order to determine the optimum surfactant

quantity per liter to be used, experiments were conducted by increasing the surfactant concentration until no

agglomeration occurs in the nanofluid solution.




The optimum quantity of surfactant is found to be 2.5ml/L after conducting pilot experiments. The sample is

then positioned in ultrasonic sonicator for 2 hours and the Nano fluids are seen to be stable even more than 24

hours without having sedimentation. The surfactant used for the present study (SPAN 20) is shown in Fig 4.5.

Fig 4.5 SPAN 20 Surfactant

Al2O3 nano fluids of five different volume concentrations in the range of 0.004, 0.008, 0.011, and

0.015 % are prepared for measuring the temperature dependent thermal conductivity of all nano fluids

concentrations. Normally agglomeration of nano particles takes place when nano particles are suspended in the

base fluid. All test samples of Al2O3 nano fluids is used for estimating their properties were subjected to the

magnetic stirring and followed by sonication process for about 1 hour.

Fig 4.6. ultrasonic-sonicator




[ ]

The Al2O3 nano fluids samples thus prepared are kept for observation and no particle settlement was

observed at the bottom of the flask containing Al2O3 nano fluids even after few hours.

Estimation of Nano particles volume concentration

In this experiment, we are considering Al2O3 nano fluid. The weight of the nano particles for a

particular volume concentration can be measured by using the formula:

𝐀𝐀𝐀2𝐀3

% Volume concentration = 𝐀𝐀𝐀2𝐀3 𝐀𝐀𝐀2𝐀3 𝐀𝐀𝐀

[ 𝐀𝐀𝐀2𝐀3

+ 𝐀𝐀𝐀

]

𝐀𝐀𝐀2𝐀3 = Weight of 𝐀𝐀2𝐀3Nano particles

𝐀𝐀𝐀2𝐀3 = Density of 𝐀𝐀2𝐀3

Nano particles = 3.97 g/𝐀𝐀3=3970 kg/m3

𝐀𝐀𝐀 = Weight of base fluid

𝐀𝐀𝐀 = Density of base fluid = 0.78 g/c𝐀3

Table 4.3. Volume concentrations (%) of Al2O3Nano particles with their corresponding weights of

Al2O3Nano particles (gms)

S.No

Volume concentration (%)

Weight concentration (gms)

1. 0.004 0.2

2. 0.008 0.4

3. 0.011 0.6

4. 0.015 0.8




Fig4.7 Sample nano fluid of Al2O3 by adding surfactant

Determination of 𝐀𝐀𝐀𝐀𝐀 nano fluid properties

Some of the important properties needed for estimation of convective heat transfer coefficient of nano

fluids are its density, thermal conductivity. The thermal properties of Al2O3 nano fluids are estimated

experimentally for all the concentrations and the results obtained in the experiment.

Density of 𝐀𝐀𝐀𝐀𝐀 nanofluids

The density of the Al2O3 nano fluids for all volume concentrations and the wquation was developed by

the Pak and Cho [1998] for nano fluids, which is stated as follows

nf p 1bf

Where

,

nf

=

Density of Al2O3 nano fluid kg/m3

=

Al2O3 nano particle volume concentration

bf = Density of base fluid kg/m3

p = Density of nano particles kg/m3




Fig 4.4 Density of Al2O3 nano fluids after calculated

S.no %Volume concentration () Density (kg/m3 )

1 0.004 802.724

2 0.008 817.448

3 0.011 825.991

4 0.015 833.715

Thermal conductivity

Thermal conductivity is the most important factor than can be investigated to prove the heat transfer

enhancement of a prepared nano fluid. Several mechanism for this strange enhancement of thermal conductivity

have been discussed. [52] The effective thermal conductivity increment may also depends on the shape of Nano

particles. Al2O3 nano particles have 20% of enhanced thermal conductivity with dispersed in transformer oil at

4 vol% concentration. Maximum enhancement of 10.7% was found at 0.10wt% in water based copper nano

fluid. [53] Alumina nano fluid and found increasing thermal conductivity with an increase in nano particles

loading, in the experimental range of concentration.

Fig 4.8 Thermal conductivity equipment




6000

5000

4000

3000

2000

1000

0

30 40 50

Temperatue

60 70

Table 4.5 calculated values of thermal conductivity

S.No Temperature

(T)

Velocity (Vs) (m/s) Thermal conductivity(k) w/mk

°C K V1 V2 V3 V4 K1 K2 K3 K4

1 30 303 1108 1035 1089 1080 0.084 0.085 0.087 0.089

2 40 313 1114 1160 1113 1088 0.086 0.087 0.088 0.0896

3 50 323 1117 1190 1179 1114 0.0885 0.093 0.094 0.096

4 60 333 1189 1228 1198 1194 0.092 0.094 0.095 0.096

5 70 343 1262 1270 1275 1335 0.097 0.10 0.102 0.105

Fig 4.9 Temperature and velocity

Fig 4.10Temperature and thermal conductivity

0.45

0.4

0.35

0.3

0.25

0.2

0.15

0.1

0.05

0

303 313 323

Temperature

333 343

Ther

mal

co

nd

uct

iviy

V

elo

city




Working of Nano fluid Interferometer

Nano fluid Interferometer also called ultrasonic interferometer a simple device from which one can

determine the velocity of ultrasonic sound in liquid medium.

1. In ultrasonic interferometer, the ultrasonic waves are produced by the piezoelectric method.

2. In a fixed frequency variable path interferometer, the wave length of the sound in an experimental

liquid medium is measured. From this, one can calculate its velocity through that medium.

3. The apparatus consists of an ultrasonic cell, which the double wall brass cell with chromium plated

surfaces having a capacity of 10ml.

4. Double wall water circulation around the experimental medium to maintain it at a known const.

temperature.

5. The micro meter scale is marked in units of 0.01mm and has an overall length of 25mm.

6. Ultrasonic waves of known frequency are produced by a quartz crystal which fixed at the bottom of

cell.

7. There is movable metallic plate parallel to the quartz plate, which reflect the waves.

8. The waves interfere with their reflections, and if the separation between the plate is exactly an integer

multiple of half wave length of the sound, standing waves are produced in the liquid medium.

9. Under these circumstances, acoustic resonance occurs. The resonant waves are a maximum in

amplitude, causing a corresponding maximum in the anode current of the piezoelectric generator.

10. If we increase (or) decrease the distance by exactly one half of the wave length (λ/2) (or) an integer

multiple of one half wave length the anode current again becomes maximum

If ‘d’ is the separation between successive adjacent maxima of anode current, then d = λ/2

We have the velocity (v) of a wave is related to its wave length (λ) by the relation.

V = λf

Where, f is the frequency of the wave.

Procedure

1. Remove the top reflector assembly from the nano fluids cell and pour liquid into the cel and screw the

knurled top.

2. Liquid should be filled, while keeping the cell out of circular base and wire out excess liquid

overflowing from the cell.

3. Insert three cell in the base and tight with the screw provided.

4. Connect the base to wave generator by co-axial cable provide with the instrument.




2

5. Keep the 𝐀1 at the middle approx and 𝐀2 knots at max position. Now move the micrometer slowly in

either clockwise or anti clockwise direction.

6. Digital micrometer will show change in reading. If the reading shows minus then it may be shifted to

plus with 𝐀2 knob.

7. Note the readings of micrometer corresponding to the maximum in digital micro-ammeter.

Formulae

Pitch scale reading (P.S.R) =𝐀1 mm Head scale reading (H.S.R) = 𝐀2 mm Least count (L.C) = 0.001mm

Micrometer reading corresponding to maximum = (P.S.R + (H.S.R*L.C))

= (𝐀1 + (𝐀2*L.C)) mm

Thermal

conductivity

′ 𝐀

Where

𝐀 3

K = 3 ∗ ( ) 𝐀𝐀

∗ K ∗ 𝐀𝐀 (4.1)

𝐀𝐀 = Avagadro number = 6.023 ∗ 1023

𝐀𝐀 = molar volume = m/ρ

K = Boltzmann constant = 1.3807 ∗ 10−23

𝐀𝐀 = ultrasound velocity

d = λ/2,V = λf

λ = 2d = (2/n)*d, (where n = 5)

f = frequency of wave = 2MHz = 2 ∗ 106

Table 4.6 results of thermal conductivity with volume concentration of 𝐀𝐀2𝐀3

S.No Volume concentration (%) Density(ρ)

kg/m3

Thermal conductivity (k)

w/mk

1 0.004 801.724 0.08625

2 0.008 814.448 0.0875

3 0.011 823.991 0.0928

4 0.015 836.715 0.0942




Thermal conductivity behaviour with Al2O3

Thermal conductivity of base fluid and Al2O3-EDM oil Nano fluid at different concentrations (0.004%,

0.008%, 0.011% and 0.015%).it is observed that thermal conductivity increases with increase in concentrations

of Nano fluids. It is because of the fact that the Ultrasonic velocity increases with increase in concentrations of

nanofluids. From the Bridgeman relation as shown in equation 4.1, it is clear that ultrasonic velocity is

proportional to the thermal conductivity. As a result of this, there is an enhancement in the thermal conductivity.

Fig 4.11. Thermal conductivity vs density

Finally, thermal conductivity increases with the increases of temperature. It is just because of increase in

thermal conductivity is mainly due to the Brownian movement of nanoparticles using Al2O3 – EDM oil as a

dielectric.

Conclusion

Generally a dielectric fluid have high thermal conductivity. High thermal conductivity implies more

amount of heat removal from tool and workpiece and cool the machining zone. The following conclusions are

drawn from the characterization.

1. Increase in the Al2O3 nanoparticle concentration enhances the thermal conductivity of nanofluid system.

0.093

0.092

0.091

0.09

0.089

0.088

0.087

801.724 814.448 823.991 836.715

Density kg/m3

The

rma

l co

nd

uct

ivit

y(k)

w

/mk




Chapter 5 Experimental Details




Selection of materials Electrode based Parameters

EDM electrode material need to have properties that easily allow charge and yet resist the erosion that

the EDM process encourages and stimulates in the metals it machines. Alloys have properties which provide

different advantages based on the needs of the application.

Table 5.1 selection of different types electrode in EDM

S No. Electrode Usage Results/Applications

1.

Cu and Cu

Alloys

1. Better EDM wear resistance than brass

2. It is more difficult to machine than either

brass or graphite.

3. It is also more expensive than graphite.

4. Cu is a base material because it is highly

conductive and strong.

It is useful in EDM

machining and gives fine

surface finish.

2.

Brass

1. It does not resist wear as well as Cu or

Tungsten.

2. It can be used in EDM wire cutting

process.

3. It need not to provide wear or arc erosion

resistance.

It is much easier to

machine and can be die

cast applications.




3.

Cu Tungsten

1. It is very expensive compared to other

electrode materials.

It is useful in making de

slots under poor

flushi condition and

also used resistance

welding electro and

some circuit wea

applications.

4.

Molybdenum

1. It is used in EDM wired machine.

2. It is the wire of choice for small slotwork.

3. It exhibits high tensile and good

conductivity.

Small diameter wired is

needed for demanding

applications and also

requiring exceptionally

small cornered radii.

5. Tellurium

Copper

1. Used in EDM machining application.

2. It is similar to brass and better than pure

copper.

It gives fine surface finish.

The performance of die sinking EDM due to shape configuration of the electrode. The effect of the

electrode shape on MRR, EWR, WR, Ra have been investigated for mild steel work materials and copper

electrode. The shape of the electrodes were round, square, triangular and diamond of constant cross sectional

area of 64 mm2.debris produced due to machining. PMESM has a different machining mechanism from the

conventional ESM. In this process, a suitable material in the powder form is mixed into the dielectric fluid of

ESM [54].

Electrode Properties

1. High Electrical Conductivity- Electrons are cold emitted more easily and there is less bulk electrical

heating.

2. High Thermal Conductivity- For the small heat load, the local temperature rise would be less due to

faster heat conducted to the bulk of the tool and does less tool wear.




3. Higher density – For the same heat load and the same tool wear by weight there would be less volume

removal or tool wear and thus less dimensional loss or inaccuracy.

4. High Melting Point- High Melting Point leads to fewer tools wear due to less tool material melting for

the same heat load, easy to manufacture, less in cost.

Work piece material

Normally HCHCR or AISI D3 consists carbon of 2% and Chromium of 12% .This is a direct hardening

material and can be hardened to 58-60 HRC. This material is used for manufacturing press tools and sheering

blades. Because the material is so tightly held and controlled in this setup, part flatness remains very true,

distortion is nearly eliminated, and edge burr is minimal. AISI D3 Die steel was used as work piece material.

Sample of size 30cm*30cm*6mm were prepared by using EDM. The prepare sample were heat treated to

improve their hardness. Table shows the chemical composition of work piece material. Typical applications for

D3 Steel:

1. Blanking and forming dies

2. Forming rolls

3. Press tools

4. Punches

5. Bushes

Table5.2 - The chemical composition of AISI D3 dies

Element Weight (%)

Carbon (C) 2-2.3

Manganese (Mn) 0.25-0.5

Sulfur (S) 0.056

Silicon (Si) 0.26

Phosphorous (P) 0.038

Chromium (Cr) 11-13

Molybdenum (Mo) 0.08

Iron (Fe) Balance




Table 5.3 Properties of the AISI D3 Die Steel

Mechanical properties

Density 7670 kg/m3

Electrical resistivity 72 µΩ-cm

Specific heat 0.5 J/g ° C

Thermal conductivity 20 W/m-K

Tool selection

The electrodes having the size of 9.5 cm diameter and 24 cm length were prepared out the rods of copper

for performing the experiments. After preparing the required size the face of all the electrodes was polished so

as to get good surface finish using different emery papers ranges from 220 to 2000 grit size following general

metallographic procedure. Table shows the chemical composition of copper electrode.

Table 5.4 - The chemical composition of the Copper electrode.

Cu% Zn% Al% Bi% Pb%

99.8 0.057 0.15 0.0011 0.0008

Table 5.5 - The material properties of the Copper electrode

S.No Material Property Value

1 Thermal Conductivity (W/mK) 391

2 Density (g/cc) 1083

3 Melting Point (°C) 1085

4 Electrical Resistivity (Ω cm) 1.69

5 Specific heat capacity(j/gm°C) 0.385




Dielectric Used

Dielectric fluids with powder particle offers significantly better thermal properties relative to those of

conventional dielectric fluids. In the powder mixed ESM powder of different materials are mixed in dielectric

fluid. The floating particles impede the ignition process by creating a higher discharge probability and lowering

the breakdown strength of the insulating dielectric fluid. As a result, MRR, SR is increased, sparking efficiency

is improved. The nano powder suspended in dielectric medium increases the gap between tool and workpiece

which in turn causes the stability of the process, thereby increasing the machinability.

H.K. Kansal proved that PMESM holds a bright promise in application of ESM, particularly with regard to

process productivity and surface quality of workpiece.

EDM oil is used as a dielectric fluid for all the experiments. Some of the properties and characteristics of

Dielectric fluid.

1. It depends upon its various chemical and fluidic properties

2. It should have high flash point, which provided a safer working environment.

3. It should have low viscosity.

4. EDM fluids should have a flash point above 180°C. Usually the higher the flash point, the higher the

viscosity. That is why we selected EDM OIL as a Dielectric in EDM machining.

5. Oxidation Stability is a measure of the dielectric fluids tendency to react with oxygen.

6. Acid number is used to quantify the amount of acid present in a sample of dielectric oil.

7. Pour point of oil is the temperature below which the oil no longer pours freely.

Table 5.6 properties of dielectric

Density(kg/m3) Sp. Gravity

789 0.820

FLASH AND FIRE POINT

The EDM oil will not ignite by itself, there must be a flame or spark present. In addition, EDM oil at it’s

flash point will not burn continuously as it will only ‘flash’ or burn for a moment. The fire point is the temperature

at which the vapor concentration of a fluid is sufficient to sustain a fire. Generally, the higher the flash point the

safer the fluid. Depending on your application, such as fine finishing, you may want a lower viscosity fluid which

will sacrifice flash point. Fine finishing with low amps will require a low viscosity fluid because your gap will

be narrow. Higher amp projects, such as roughing, will require a high flash point and the viscosity is not of a

major concern.




Table 5.7 characteristics of EDM oil.

S.No Characteristics Values

1 Appearance Bright and Clear

2 Density @ 30 (g/cc) 0.78

3 Flash point (°C) >180

4 Pour point (°C) -9

5 Viscosity @ 100 F 32.6

6 Dielectric Strength

(kV/m)

45

Experimentation

The working tank of ESM machine has the dimensions of 800mm X 500mm X 350mm occupying

400lts. It needs large amount of nanopowder for mixing in such large tank of ESM to obtain desired powder

concentration in dielectric fluid for operation. Also, clogging takes place when nanopowder blended dielectric

is filtered with the existing filtering system. So, to overcome these difficulties, a new tank, having volume of 3

liters has been chosen for conducting experimentation.

All the experiments were conducted on a die sinking EDM machining setup as shown in Fig.5.1. The

dielectric fluid with varying concentrations of powder for every experiment, a separate dielectric circulation

system was designed, fabricated and attached to the existing machine as indicated in Fig.5.2. The pump receives

the dielectric fluid from the outlet of the cylindrical tank and recirculates it to the tool-work inter electrode gap

to flush out the debris. The continuous circulation of the dielectric fluid avoids the settlement of powder

particles in the flushing system. In the current investigation, side jet flushing was selected to flush out the debris.




Fig 5.1 EDM equipment

Setup arranged inside the EDM machine

Fig 5.2 Experimental setup

Experimental details

Table 5.8 Details of experiment

Experimental Conditions Descriptions

Workpiece AISI D3 Steel

Electrode material ELECTROLYTIC COPPER

Powder type Alumina (Avg. Size 50 nm)

Working time (Mins) 20

Powder concentration (g/l) 0,0.2,0.4,0.6,0.8

Peak current (Amps) 2,4,6,8,10

Pulse ON time (µsec) 100,200,300,400,500

Gap voltage (V) 40,50,60,70,80




Dielectric fluid EDM oil




Design used for experiments

To perform a designed experiment, changes are made to the input variables and the corresponding

changes in the output variables are observed. Because each variable has 5 levels hence, it would require large

number (i.e 54 = 625) of combinations to assess the performance of nano powder blended ESM. Conducting

these many experiments requires lot of manual effort and increase the cost. To overcome these difficulties

Design of Experiments (DoE) techniques is the best choice.

The experiments were designed according to central composite design (CCD) of response surface

methodology (RSM). Response Surface Methodology has effectively been applied to study and optimize the

processes. It divides into small number of experiments and also detect the interaction effect of the independent

parameters on the response. The process parameters and their levels are provided in Table 5.9. STATISTICA

software was used to plan the experimental design. Standard design with 4 factors consisting of 16 factorial

points, 8 axial points and 2 center points. According to the experimental design, 26 number of runs was obtained.

The runs in terms of coded values are tabulated in Table 5.9. Each run is carried out for 20 mins and is repeated

thrice to reduce measurement error.

Table 5.9 Experiments are planned to be conducted

Standard

order

Run

Powder

concentration (Cp)

Peak

current (Ip)

Pulse on

time (Ton)

Gap voltage

(Vp)

17 27 0 6 300 60

1 9 0.2 4 200 50

9 19 0.2 4 200 70

5 17 0.2 4 400 50

13 26 0.2 4 400 70

3 3 0.2 8 200 50

11 21 0.2 8 200 70

7 12 0.2 8 400 50

15 5 0.2 8 400 70

19 7 0.4 2 300 60

21 29 0.4 6 100 60

23 25 0.4 6 300 40

25 1 0.4 6 300 60

27 6 0.4 6 300 60

26 8 0.4 6 300 60




29 18 0.4 6 300 60

28 22 0.4 6 300 60




30 24 0.4 6 300 60

24 20 0.4 6 300 80

22 13 0.4 6 500 60

20 11 0.4 10 300 60

2 14 0.6 4 200 50

10 23 0.6 4 200 70

6 4 0.6 4 400 50

14 15 0.6 4 400 70

4 30 0.6 8 200 50

12 2 0.6 8 200 70

8 28 0.6 8 400 50

16 0 0.6 8 400 70

18 16 0.8 6 300 60

𝐀𝐀𝐀𝐀𝐀 Properties

Particle size is an important physical parameter in nano fluids because it as suspension stability of Nano

particles. Nano fluids have been trying to exploit the unique properties of nano particles to develop stable as

well as highly conducting heat transfer fluids. Thus nano suspensions show high thermal conductivity possible

due to enhanced convention between the solids particle and liquid surfaces. Due to lower dimensions, the

dispersed Nano particles can behave like a base fluids molecule in a suspension, which helps us to reduce

problems like particle clogging, sedimentation, etc. found with micro particles suspensions.

Chemical properties of 𝐀𝐀𝐀𝐀𝐀 nano particles

Table 5.10 properties of Al2O3 nano powder

𝐀𝐀2𝐀3 CaO 𝐀𝐀2𝐀3 MgO 𝐀𝐀𝐀2

>99.9% <0.017 <0.035 <0.001 <0.005




Fig 5.3 Photographic view of Al2O3Nano particles

Metal Removal Rate (MRR)

Weight of the workpiece before and after the experiment was measured using an electronic balance.

Time duration of each experimental run was recorded using a digital stop watch and was used to calculate the

MRR.

MRR = (𝐀𝐀−𝐀𝐀)

ρ∗ 𝐀 (5.1)

Wb = weights of the specimen before the machining and

Wa = weights of the specimen after the machining

ρ = density of workpiece material

T = machining time




Fig 5.4 machined workpieces at different machining conditions




Surface Roughness

Surface roughness of the machined work pieces were measured using surface roughness tester. The

surface roughness is represented by the center line average method (Ra). Roughness measurements were carried

out in the longitudinal, transverse direction on the machined surface. Measurements were repeated three times

for better accuracy and average values are calculated. The instrument used to measure the surface roughness is

shown in Fig 5.5. The surface roughness is calculated by the center line average method (Ra). It is defined as

the average departure of roughness profile from the center line. The expression of Ra isgiven in equation 5.2.

R 1

a l

y(x).dx (5.2)

where l is the sampling length, y is height of peaks and valleys of roughness profile and x is the profile direction.

The average of three values was taken as the surface roughness of a particular specimen. The instrument used

to measure the surface roughness is shown in Fig 5.5.

Fig 5.5 surface roughness tester

Experimentation procedure

1. In EDM, die is sinking type and straight polarity is used to conduct experiment.

2. Manufacture separately, mild steel container in EDM actual tank.

3. Attach the motor stirrer to the machining tank.

4. The copper electrode with 24 cm and 9.5 diameter is fixed in servo feed tool holder of EDM machine.

5. Work piece in the dimension of 30*30cm and thickness is 6mm.

6. Check the alignment vertically and horizontally by the dial indicator.

7. Weight the work pieces by using digital weighing machine, before and after experimentation.

8. Fill the dielectric oil of 2litres and the equipment is placed in the machining tank.

9. Switch ON the machine.




10. Powder is added to the dielectric on work material and MRR is calculated.




Chapter 6 Results and discussion




Results are calculated

Table 6.1 plan of experiments with results of MRR

Standard

order

Run

Powder

concentration

(Cp)

Peak

current

(Ip)

Pulse on

time

(Ton)

Gap

voltage

(Vp)

MRR

(mm3/min)

17 27 0 6 300 60 1.884

1 9 0.2 4 200 50 1.910

9 19 0.2 4 200 70 1.953

5 17 0.2 4 400 50 1.879

13 26 0.2 4 400 70 1.848

3 3 0.2 8 200 50 1.972

11 21 0.2 8 200 70 2.416

7 12 0.2 8 400 50 2.147

15 5 0.2 8 400 70 2.434

19 7 0.4 2 300 60 0.849

21 29 0.4 6 100 60 1.810

23 25 0.4 6 300 40 1.829

25 1 0.4 6 300 60 1.482

27 6 0.4 6 300 60 1.482

26 8 0.4 6 300 60 1.482

29 18 0.4 6 300 60 1.482

28 22 0.4 6 300 60 1.482

30 24 0.4 6 300 60 1.482

24 20 0.4 6 300 80 1.837

22 13 0.4 6 500 60 3.291

20 11 0.4 10 300 60 4.564

2 14 0.6 4 200 50 2.425

10 23 0.6 4 200 70 1.455

6 4 0.6 4 400 50 2.408

14 15 0.6 4 400 70 2.251

4 30 0.6 8 200 50 2.169

12 2 0.6 8 200 70 2.067

8 28 0.6 8 400 50 2.281

16 0 0.6 8 400 70 2.013

18 16 0.8 6 300 60 1.987




Influence on Peak current Vs MRR

Fig 6.1 peak current vs MRR

MRR increases with peak current due to an increase in discharge energy. The increase in peak current

also increases the number of electrons and ions per unit volume, thereby increasing the pressure in the plasma

channel. As a consequence, impulsive force per unit area (specific impulsive force) increases allowing an easier

ejection of the molten material.

Influence on Pulse on time vs MRR

The higher Ton has increased MRR and the decrease of MRR after 0.6 g/l could be attributed to short

circuit at higher powder density which causes the machining process to become uneven condition to the net

reduction in MRR.

The higher Ton has decreased MRR for all conditions of Ip with Cu electrode. The reason is with a

constant setting of 80% duty factor, the pulse interval will increase with the increment of Ton. This high ignition

delay due to high pulse interval reduces the machining rate, thus MRR is decreased. The intensity of energy

release during sparking is proportionally increased whereby higher temperature produced by the spark, melts

more material and removes from the workpiece. (Ghewade and Ninapikar,2011)




.

Fig 6.2 pulse on time vs MRR

Influence on Powder concentration vs MRR

The effect of powder concentration on MRR, the MRR was decreased by increasing the powder

concentration into the dielectric fluid. Addition of an appropriate amount of additives into the dielectric fluid of

EDM causes greater erosion of the material. The reason for the enhancement of MRR at higher powder

concentration is mainly attributed to a reduction in the breakdown strength of the dielectric fluid leading to

early spark, and increase in frequency of sparking within the discharge (Kumar et al, 2010).

Fig 6.3 powder concentration vs MRR




Influence on Gap voltage vs MRR

When MRR increases with increase of gap voltage because the time required for bridging the discharge

gap with ions and electrons increases due to an increased spark gap resulting in low MRR. Less energy density

and energy loss in the discharge gap also decrease the MRR (S. Assarzadeh, M. Ghoreishi).

Fig 6.4 gap voltage vs MRR




Results are calculated

Table 6.2 plan of experiments with results of SR

Standard

order

Run

Powder

concentration

(Cp)

Peak

current(Ip)

Pulse on

time

(Ton)

Gap

voltage(Vp)

SR

(µm)

17 27 0 6 300 60 4.00

1 9 0.2 4 200 50 4.78

9 19 0.2 4 200 70 4.50

5 17 0.2 4 400 50 4.53

13 26 0.2 4 400 70 4.78

3 3 0.2 8 200 50 5.36

11 21 0.2 8 200 70 5.08

7 12 0.2 8 400 50 4.79

15 5 0.2 8 400 70 5.36

19 7 0.4 2 300 60 4.12

21 29 0.4 6 100 60 4.58

23 25 0.4 6 300 40 4.52

25 1 0.4 6 300 60 4.07

27 6 0.4 6 300 60 4.07

26 8 0.4 6 300 60 4.07

29 18 0.4 6 300 60 4.07

28 22 0.4 6 300 60 4.07

30 24 0.4 6 300 60 4.07

24 20 0.4 6 300 80 4.57

22 13 0.4 6 500 60 4.15

20 11 0.4 10 300 60 3.9

2 14 0.6 4 200 50 3.8

10 23 0.6 4 200 70 3.79

6 4 0.6 4 400 50 3.59

14 15 0.6 4 400 70 3.93

4 30 0.6 8 200 50 4.02

12 2 0.6 8 200 70 4.28

8 28 0.6 8 400 50 4.28

16 0 0.6 8 400 70 5.08

18 16 0.8 6 300 60 3.81




Influence on Powder concentration vs SR

The similar condition also can be observed when the highest Powder concentration 0.2g/l was applied.

At powder concentration 0.2g/l, the surface roughness was increased as the peak current and pulse on time

increases. At very high concentrations, the dielectric loses its ability to distribute uniformly all the powder

materials. Therefore, powder settling is a common problem at higher concentration, although spark gap increases.

In addition, at higher concentration of alumina nano-powder, the bridging of powder particles may occur, which

results in arcing and short-circuiting more frequently (Jahan et al, 2011)

Fig 6.5 Powder concentration vs SR

Influence on Peak current vs SR

At powder concentration 0.2g/l the surface roughness was increased as the peak current increases and

surface roughness was decreased as the pulse on time increases as shown in Fig 6.6 and 6.8. At very high

concentrations, the dielectric loses its ability to distribute uniformly all the powder materials. Therefore, powder

settling is a common problem at higher concentration, although spark gap increases. In addition, at higher

concentration of alumina nano-powder, the bridging of powder particles may occur, which results in arcing and

short-circuiting more frequently (Jahan et al, 2011).




Fig 6.6 peak current vs SR

Influence on Pulse on time vs SRR

Fig 6.7 pulse on time vs S

Influence on Gap voltage vs SR

SR also decreases with pulse-on time due to aforesaid reasons. Short-circuiting and incomplete removal

of debris from the discharge area make the process unstable and degrade the surface

quality at high pulse-on times. More debris is formed and adheres to the machined surface as the

pulse-on time increases the productive machining time.




Fig 6.8 Gap voltage vs SR




Chapter 7 Conclusions and Future scope




Conclusion

In the current research work, the effect of powder-mixed ESM (PMESM) process parameters were

calculated on temperature distribution, MRR and SR considering AISI D3 Die steel as workpiece material.

After gaining initial information on the Al2O3 nano powder on the process, experimental investigation was

carried out according to RSM-based design of experiment. The MRR values are obtained from powder-mixed

dielectrics were very close to each other. Careful observation would indicate that alumina has produced highest

MRR and followed by decrease of surface roughness, within the considered process parameter range.

1. MRR and surface roughness decreases with the increase in powder concentration because it increases the

number of electrons and ions per unit volume, thereby increasing the pressure in the plasma channel.

2. MRR and SR increases with increase of peak current due to an increase in discharge energy.

3. MRR increases with increase of gap voltage because the time required for bridging the discharge gap with

ions and electrons increases due to an increased spark gap resulting in low MRR.

4. SR decreases with increase of Pulse on time due to very high concentrations of the dielectric loses its ability

to distribute uniformly all the powder materials.

5. SR decreases with increase of Gap voltage which occurs due to Short-circuiting and incomplete removal of

debris from the discharge area make the process unstable and degrade the surface quality at high pulse-on times.

Future Scope

1. Modelling and simulation can be extended for different aspects of surface integrity such as surface

roughness, altered layer thickness and crack formation.

2. Optimal parameter settings for achieving optimal responses can be carried out for

individual powders using suitable optimization technique.

3. Influence of nano powders on the PMEDM processing of AISI D3 Die steel in particular can be

investigated in comparison with PMEDM using micro powders.




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