simulation studies of impact of electrode ... no direct contact between tool and workpiece. in...

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 7, Issue 4, July–Aug 2016, pp.196–204, Article ID: IJMET_07_04_020

Available online at

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ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication

SIMULATION STUDIES OF IMPACT OF ELECTRODE

GEOMETRY ON THERMAL PROFILES IN MICRO

EDM BY USING CFX TOOLS

J.S.Uday Kumar

M. Tech Student, Dept. of Mechanical Engineering

GMR Institute of Technology, Rajam

Srikakulam, A.P – 532127, India

Dr. CLVRSV Prasad

Professor, Dept. of Mechanical Engineering



K.Santa Rao

Assistant Professor

Dept. of Mechanical Engineering



ABSTRACT

Electrical discharge Machining (EDM) is a non customary machining process and it removes

the metal with sparks. EDM is capable of machining hard material components which is difficult to

machine. A copper electrode is used to machine the workpiece and to obtain the replica of tool

electrode Shape on workpiece without direct contact. The machining parameters in EDM affect

machining outputs such as MRR and electrode wear. Material removal rate (MRR) in edm also

depends on the thermal profiles generated in the workpiece. In the current work, an attempt has

been made to study the impact of tool electrode contours on the thermal profiles which inturn

influence the MRR. The thermal profiles for various machining parameters and tool geometries are

simulated using CFX tools. The simulated results which are found different for different tool

geometries are validated by conducting the experimentation on SINKER EDM machine.

Key words: Thermal Profiles, Tool Geometry, EDM, Simulation, Single Spark Discharge

Cite this Article: J.S.Uday Kumar, Dr. CLVRSV Prasad and K.Santa Rao, Simulation Studies of

Impact of Electrode Geometry on Thermal Profiles In Micro EDM by Using CFX Tools.

International Journal of Mechanical Engineering and Technology, 7(4), 2016, pp. 196–204.

http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=7&IType=4

Simulation Studies of Impact of Electrode Geometry on Thermal Profiles In Micro EDM by Using CFX Tools


INTRODUCTION

Micro- EDM is one of widely used techniques in manufacturing purposes. The material removal rate in

EDM mainly depends on the amount of electrical energy supplied between tool and workpiece. There will

be no direct contact between tool and workpiece. In general, EDM is machined with single spark

discharge. Dibitonto et al. [1] used a point heat source model to develop a spark on the surface of the

workpiece. Patel et al. [2] used the discharge power of the plasma as a heat source between tool and

workpiece. In a study, Kansal et al. [3] introduced a two dimensional axi symmetric model for powder

mixed dielectric using FEM technique. This developed model evaluates the temperature distribution of the

workpiece with the help of ANSYS software. The obtained temperature profiles helps to predict the

material removal rate and the the simulation results are compared with the experimental results. Yadav et

al. [4] investigated the thermal strain behaviour after the spark developed on the workpiece surface. Van

Dijck et al. [5] deliberated about the profiles of the temperatures at the workpiece surface by using

transient thermal analysis. Kumar [6] had checked the thermal strains approaches and also micro cracks

behaviour on workpiece surface using the mode of heat transfer through conduction. Heat loss by radiation

and other forms are neglected. The energy dissipated into the workpiece is 18 to 20% of total discharge

channel energy. It is concluded that experimental values are similar to the theoretical results. After a

thorough study of literature mentioned above it has been found that there is no study reported on

simulation and experimental validation relating the temperature profiles varying with the geometry of tool

used in electric discharge machining. In order to fill this gap observed from the literature the simulation

has been done with a combination of Stainless Steel 316L as a workpiece material and Copper as a

electrode by means of Transient thermal analysis in ANSYS V14.5 with a single spark discharge of 100µs

with three different geometries of the electrode in current investigation. In each case, the temperature

distribution is verified for a discharge of 100µs pulse.

PROBLEM DEFINITION

In the current study, an attempt has been made to simulate the temperature distribution for different

geometries of the electrode using Transient thermal analysis. In this thermal analysis, Guassian heat model

is used to find out the temperature distribution of workpiece surface. The simulation has been done

presuming that cross section area is same and machining conditions are maintained constant for all the

geometries of the electrode. The tool contours preferred for the simulations are circle, Square and triangle.

The results obtained in the simulation are validated by conducting experiment for the same workpiece

tool combination on sinker EDM machine.

METHODOLOGY

SIMULATION

The steps involved in simulation include Geometric modeling, Meshing, Applying Boundary conditions,

results of the simulation. In the first step, the geometric modeling (3D analysis) is taken into consideration

and the dimensions of the workpiece material is taken as 40 × 40 × 10 mm3. Based on literature available,

stainless steel 316L is preferred for the workpiece and copper is chosen for electrode. Table 1 depicts

material properties of workpiece and tool in regard to thermal analysis.

Table 1 Material properties of Workpiece and Tool

COPPER (Electrode) Stainless steel 316L (Workpiece)

Density (Kg/m3) 8933 8000

Thermal conductivity (W/mK) 400 18

Specific heat (J/KgK) 385 530

J.S.Uday Kumar, Dr. CLVRSV Prasad and K.Santa Rao


Based on the dimensions of the work piece, tool dimensions are selected for circle, square, triangle in

such way that the cross section remains constant for all the three. 3D modeling is done in all the three cases

and meshing of the part is done by using automatic method. In the second step, the boundary conditions are

applied to the workpiece by assuming a set of machining conditions. The boundary conditions are taken in

such a way that, across the contact surface of the tool and the work piece, the mode of heat transfer is

assumed to be conduction. Within the work piece the heat transfer is assumed to be the combination of

conduction and convection. Within the work piece, it is assumed to be conduction and from the workpiece

to the electrolyte, it is assumed to be convection. The lateral faces and the bottom faces of the workpiece

are assumed to be perfectly insulated and maintained at 27 ºc i.e., 300K. The highest temperature for

conduction is taken as 20,000 K and for the convection, the ambient temperature is taken as 27 ºc i.e.,

300K. The convective heat transfer coefficient is taken as h= 5w/m²k. Fig.1 shows different geometries of

electrode modeled in ANSYS Workbench.

a

b

c

Figure 1 Different tool Geometries: (a) Circle, (b) Square, (c) Triangle

Meshed geometries, Temperature distributions of the geometries are depicted in Fig. 2 and Fig. 3

respectively. Temperature distributions along the downward vertical axis in geometries considered are

shown in Fig. 4.

Simulation Studies of Impact of Electrode Geometry

http://www.iaeme.com/IJMET

a

Figure 2 Meshing for different electrodes

a

Figure 3 Temperature distributions f

f Electrode Geometry on Thermal Profiles In Micro EDM

IJMET/index.asp 199

b

c

Meshing for different electrodes: (a) Circle, (b) Square, (c) Triangle

b

c

Temperature distributions for different electrodes: (a) Circle, (b) Square, (c) Triangle

n Thermal Profiles In Micro EDM by Using CFX Tools

[email protected]

: (a) Circle, (b) Square, (c) Triangle

: (a) Circle, (b) Square, (c) Triangle



Figure 4 Temperature distributions obtained in different geometries

0

10000

20000

30000

0 417 1040 1670 2290 2920 6040Tem

per

ature

[K

]

Distance between successive thermal gradients

[µm]

Circle

0

5000

10000

15000

20000

25000

0 417 1040 1670 2290 2920 6040

Tem

per

ature

[K

]

Distance between successive thermal gradients [µm]

Square

0

5000

10000

15000

20000

25000

0 376 2630 4510 6760 8260 9770

Tem

per

ature

[K

]

Distance between successive thermal gradients

[µm]

Triangle



Table 2 Maximum and Minimum Temperatures of geometries considered

S. No Geometry Max. Temp

(Kelvin)

Min. Temp

(Kelvin)

1. Circle 20000 295.15

2. Square 20000 293.13

3. Triangle 20000 290.17

As per the literature review, the MRR is proportional to the thermal profile. The simulated thermal

profiles obtained for circular, square and triangle geometry of the tools shows that the temperature

variation is different for the three geometries. This indicates that MRR is relatively higher in circle and

lower in triangle.

EXPERIMENTAL VALIDATION

To check the correctness of the values obtained from the simulation, experiments have been conducted on

SINKER EDM available in the department. The machine is shown in Fig. 5 and its specifications are

mentioned in Table 3.

Figure 5 SINKER Electric Discharge Machine

In order to maintain consistency workpiece dimensions both in simulation and experimentation are

kept unique. Tools of various geometries are fabricated from parent copper electrode of dimensions φ20

mm x 150 mm. Tool and 3D view of workpiece are shown in Fig. 6. Various machining parameters that

were kept constant during experimentation are presented in Table 4.



Table 3 Specifications of EDM

Work tank internal dimensions (W×D×H) 800 × 500 × 350 mm

Work table dimensions 550 × 350 mm

Traverse (X,Y,Z) 300,200,250 mm

Maximum job weight 300 Kg

Maximum Electrode weight 100 kg

Maximum job height above the table 250 mm

Feed motor/Servo system for Z axis DC servo

Position measuring system (X,Y,Z) Incremental linear scale

Dielectric medium EDM oil

Dielectric capacity 400 litres

Pulse generator S50 ZNC

Pulse generator type MOSFET

Maximum working current 50 A

Max.MRR (cu-st) 350 mm3/ min

Power supply 3 phase,415v AC,50 Hz

Connected load 6KVA

Figure 6 Tool and Three dimensional view of workpiece

Table 4 Machining parameters

Ip (Peak current) 10 amp

Ton (pulse on time) 100 µs

τ (pulse duty factor) 10

Vg (Voltage gap) 50

Sen (sensitivity) 8

Asen (arc sensitivity) 3

Tw (working time) 0.9

Rd (Retract distance) 2.5

FABRICATION OF ELECTRODES

Three electrodes have been fabricated in such a way that the contact area of tool with the work piece is

constant. For the current experimentation, the contact area to the surface is Ac=314 mm2, which is constant

for all the three profiles. The machining carried out using all the three electrodes in a sequence for a period

of 30 min, 45 min, 60 min. Based on the amount of material removed in all the experiments conducted

with the three tool profiles. It is observed that the net material removed is high in circle and low in triangle.

The following figures indicate the machining process conducted on a sinker edm.



Circle electrode Workpiece machined with a circle electrode

Square electrode Workpiece machined with a square electrode

Triangle electrode Workpiece machined with a triangle electrode

Figure 7 Fabricated tools and its respective impression on workpiece

Table 5 Difference in weights observed

S. No Geometry Before machining

(Weight in gms)

After machining

(Weight in gms)

Net material

removed (in gms)

1. Circle 121.30 117.66 3.64

2. Square 118.72 116.01 2.69

3. Triangle 120.30 118.90 1.32

VALIDATION AND CONCLUSION

The results in the simulation and the experimentation indicate the concurrence of the statement saying that

the thermal profiles influence the metal removal rate (MRR). It was observed that the MRR for circle is on

the higher side and for triangle is on lower side inline with respective thermal profiles as shown in Table 5.

This in turn confirms the statement that the tool geometry influence the thermal profile and hence MRR.



SCOPE FOR EXTENSION

The validation has been done in the current investigation for a specific workpiece tool combination of a

stainless steel 316L and copper. This can also be verified for other combinations and also at different

machining parameters. Apart from doing this additional experimentation, further investigation can also be

done to analyze theoretically the reasons for having different thermal profiles for different tool geometry.

REFERENCES

[1] DiBitonto, D. D., Eubank, P. T., Patel, M. R., & Barrufet, M. A. (1989). Theoretical models of the

electrical discharge machining process. I. A simple cathode erosion model. Journal of applied physics,

66(9), 4095-4103.

[2] Patel, M. R., Barrufet, M. A., Eubank, P. T., & DiBitonto, D. D. (1989). Theoretical models of the

electrical discharge machining process. II. The anode erosion model. Journal of applied physics, 66(9),

4104-4111.

[3] Kansal, H. K., Singh, S., & Kumar, P. (2008). Numerical simulation of powder mixed electric discharge

machining (PMEDM) using finite element method. Mathematical and Computer Modelling, 47(11),

1217–1237.

[4] Yadav, V., Jain, V. K., & Dixit, P. M. (2002). Thermal stresses due to electrical discharge machining.

International Journal of Machine Tools and Manufacture, 42(8), 877–888.

[5] Snoyes, R., & Van Dijck, F. (1971). Investigations of EDM operations by means of thermo

mathematical models. Annals of CIRP, 20(1), 35.

[6] K Santa Rao, Dr. S V Ramana and Dr. C L V R S V Prasad, Influence of Solid Lubricant Emulsions on

Surface Roughness of Hardened Steel When Machining On Shaper. International Journal of

Mechanical Engineering and Technology, 4(5), 2013, pp. 63–70.

[7] Mukesh Regmi, Anil Pol and Sachin Kulkarni, Multi Response Optimisation of Die Sinker EDM For

Alsic Composite. International Journal of Mechanical Engineering and Technology, 7(3), 2015, pp. 63–

77.

[8] A. Parshuramulu, K. Buschaiah and P. Laxminarayana, A Study On Influence of Polarity on The

Machining Characteristics of Sinker EDM. International Journal of Mechanical Engineering and

Technology, 4(3), 2013, pp. 158–162.

[9] Panda, D. K. (2008). Study of thermal stresses induced surface damage under growing plasma channel

in electro-discharge machining. Journal of materials processing Technology, 202(1), 86–95.

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