5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT

Guwahati, Assam, India

564-1

DEVELOPMENT AND EXPERIMENTAL INVESTIGATION OF ELECTRO-

DISCHARGE DIAMOND FACE GRINDING

Sanjay Singh1, Vinod Yadava

2, Ram Singar Yadav

3*

1 MED, MNNIT Allahabad, Allahabad, India, mechanist.ssp@gmail.com 2 MED, MNNIT Allahabad, Allahabad, India, vinody@mnnit.ac.in

3* MED, MNNIT Allahabad, Allahabad, India, ramsingar.ip@gmail.com

Abstract

Electro-Discharge Diamond Face Grinding (EDDFG) is an advanced hybrid machining process for face

grinding of wide variety of electrically conductive difficult-to-machine hard materials by suitable modification in

Electro-Discharge Machining (EDM). In the present work, the EDDFG setup has been developed and tested for

grinding difficult-to-machine materials and also attempted for fabrication of metal matrix composite of Aluminium

(Al) reinforced by 10% Silicon Carbide (SiCp). To perform such hybrid machining process, the developed

experimental setup was used for experimental study of EDDFG process on Al-SiCpMMCby considering the effect of

gap current, pulse on time and wheel RPM on average surface roughness (Ra) and material removal rate (MRR). The

metal bonded diamond abrasive grinding wheel is mainly responsible for higher value of MRR. It was also observed

that MRR is higher at moderate value of wheel RPM and wheel rotation improves the flushing action. The average

surface roughness (Ra) was observed better at low values of gap current, pulse on time and wheel RPM. The present

developed EDDFG setup has proven to be successful for machining of difficult-to-machine materials. Texture of the

machined surface has been studied using Scanning Electron Microscope (SEM). Keywords: Electro-Discharge Diamond Face Grinding (EDDFG),Al-SiCp MMC, MRR and Ra

1 Introduction

The growth of superior ammunitions, fighting ships,

aircraft and intercontinental ballistic missiles etc has

resulted into the development of the tailored made

advanced engineering materials, which are able to meet

the stringent operational as well as environmental load

requirements. Such advanced engineering materials are

titanium alloys, metal matrix composites and

superalloys etc. and are duly inherited with the

characteristics of high strength at elevated temperature,

resistance to chemical degradation, wear resistance and

low thermal diffusivity etc. But at the same time, these

materials do pose challenges to conventional as well as

non-conventional machining processes and these

materials are also referred as difficult-to-machine or

advanced materials. The problem associated with

conventional machining of advanced materials is the

frequent failure of the cutting tool, whereas with non-

conventional machining is lower production rate and in

few cases not even viable.

Koshy et al. (1996) have studied and suggested to

overcome the difficulties of conventional as well as non

-conventional machining processes, altogether a new

trend in machining process known as hybrid machining

processes (HMP), have been emerged and are in use at

increasing rate. In HMPs, two or more machining

processes are combined to achieve the aggregate

potential advantage of the constituent processes with

impairing the inherent disadvantage of the constituent

processes. In present case, HMP has been developed by

combining the use of metal bonded abrasive grinding

wheel with electrical discharge machining (EDM) and

termed it as Electro-Discharge Diamond Grinding

(EDDG). Grodzinskii (1979), Vitlin (1981) and

Grodzinskii&Zubotava (1982) have suggested the

concept of combination of EDM and diamond grinding,

was made in late eighties (1980) in erstwhile USSR for

machining of electrically conductive hard materials. In

this process, the metal bonded diamond wheel removes

the materials from work surface by simultaneous

influence of diamond grains and continuous discrete

electrical sparks, thereby causing the abrasion (micro-

cutting) and electro-erosion action respectively as also

shown in Figure 1.

Figure 1 Schematic representation of use of diamond

abrasives in rotating tool electrode in EDM

IEG

Spark

DEVELOPMENT AND EXPERIMENTAL INVESTIGATION OF ELECTRO-DISCHARGE DIAMOND FACE GRINDING

564-2

Ramesh and Sagar (1999) have discussedfabrication of

metal matrix composite automotive parts for the

mixtures of four different compositions (15, 20, 25 and

30% by weight) of SiC which is prepared by the Powder

Metallurgy technique, and fabricated by placing these

powder mixtures in layers in a die.

Choudhury et al. (1999) have studied the effect of

current on MRR and grinding forces for different

voltage, pulse on-time and duty factor during EDDG

process on HSS. It has been observed that tangential

grinding force decreases with increase in voltage and

duty factor for a particular value of gap current. They

have also reported the effect of process parameters on

the MRR andtestedthe feasibility of EDDG process

experimentally in cut-off grinding configurations.

Mohan et al. (2002) studied the effect of SiC and

rotation of electrode on electric discharge machining of

Al-SiC composite. The MRR was more with positive

polarity and increased with increase in current. MRR

was found more with Brass electrode in comparison

with Copper electrode. The increase of volume

percentage of SiC resulted in less MRR. The increase of

pulse duration resulted in less MRR and it was more

with increase in RPM.

Yadav et al. (2008) have observed for Electro-Discharge

Diamond Grinding (EDDG) process, developed new

experimental setup to increase the material removal rate

of the hard materials and studied the influence of

various factors on the performance characteristics, such

as current, wheel speed, pulse-on time and duty factor

on MRR.It was found that MRR is increases with

increasing current, wheel speed, and pulse on time and

decreases with the high surface finish mode of EDM on

High Speed Steel (HSS) workpiece.

Singh et al. (2010) have used Diamond abrasive in

bronze bonding material for grinding wheel and WC-Co

Composite workpiece for Electro-Discharge Diamond

Face Grinding (EDDFG) and found Improvement in

MRR by 86.49%, reduction in WWR by 21.70% but

deterioration in ASR by 14.86% have been found at the

optimum parameter setting compared to Electro-

Discharge Face Grinding (EDFG).

Abothula et al. (2010) have discussed the rotation of

non-abrasive disc shape tool electrode about vertical

axis and find improves material removal rate (MRR)

and average surface roughness (ASR) because of

effective flushing of working gap. The effect of input

process parameters of EDFG processsuch as gap

current, pulse on-time, pulse off-time and wheel speed

on MRR and ASR during machining of High Carbon

Steel and High Speed Steel workpieces, are investigated

and also compared the results with those of stationary

electrodes.

Singh et al. (2011) have studied the process synergic

interactive effect of abrasion action and electro-

discharge action. A face grinding setup for Electro-

Discharge Diamond Grinding (EDDG) process is

developed and the effect of wheel RPM, gap current,

pulse on-time and duty factor on material removal rate

(MRR), wheel wear rate (WWR) and average surface

roughness (Ra) are investigated while machining High

Speed Steel (HSS) workpiece.

Velmurugan et al. (2011) have experimentally

investigated the machining characteristics of Al6061

based hybrid metal matrix composite processed by

electro-discharge machining and observed effectson

material removal rate (MRR), tool wear rate (TWR) and

surface roughness with variation in current, pulse on-

time, flushing pressure of dielectric fluid and voltage.

Therefore no work have been reported on influence

ofinput process parameters such as wheel speed, gap

current and pulse on-timeon material removal rate

(MRR) and average surface roughness (Ra) for the

process of Electro-Discharge Diamond Face Grinding

(EDDFG) mode on Al-SiCpmetal matrix composite.

In this paper, The authors have made an attempt for

fabrication of metal matrix composite of Aluminium

(Al) reinforced by 10% silicon carbide (SiCp) particles

with grain size 600 mesh number and also developed an

experimental setup for grinding wheel rotation attached

with EDM machine. Experiments were conducted to

investigate the effect of gap current, pulse on time and

wheel RPM on material removal rate (MRR)and

average surface roughness (Ra).

2 Development of Experimental Setup

The EDDFG attachment has been designed and

fabricated with consideration of all fundamental

mechanism of the EDDFG process and basic functional

requirement of different parts with special consideration

of weight and vibration. The designed attachment has

been fitted on the ram of Smart ZNC Sinker EDM

machine (ZNC 320 Ecoline) by replacing actual tool

holder of die-sinking EDM and also tested successfully.

The preliminary experiments were conducted to find the

range of input process parameters applicable for

successful machining characteristics of EDDG process.

The EDDFG setup consist of perpendicularly

mounted (buttJoint) at one side of Al-alloy base plate of

thickness 12 mm, electrical permanent magnet direct

current (PMDC) motor of 0.25 hpRotomag (India) make

with 1500 rpm, electrically conductive tool electrode,

rotating spindle cum tool electrode holder mechanism,

mounted on the ram of EDM machine.

The housing assembly of rotating spindle has one side

pulleyand another side for holding of tool electrode. The

spindle housing is mounted on lower side of horizontal

plate and the horizontal plate has a hole through which

assemblyof rotating spindle passes. The driven pulley is

mounted on the top of the spindle.

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12

Guwahati, Assam, India

The power transmitted from electrical motor to spind

through driver pulley mounted on motor shaft and

driven pulley by ‘V’ belt of trapezoidal section.

Table 1 Specifications of different parts

The rotating spindle is supported on four

antifriction ball bearings in housing, so that axial thrust

load is taken care of and to avoid the

ofrotating spindle.The selection of these four

antifriction ball bearings is done based on the expected

load, motor power, motor RPM and endurance run.

Figure 2 Schematic diagram of EDDFG attachment

Dimensional specification of ‘V’ belt is M6

The tension is provided in V-belt to avoid slippage. The

motor is mounted on vertical Al-alloy plate

horizontal Al-alloy base plate.

Portable digital tachometer Electronic Automation

Private Ltd (EAPL), India make model: DT 200 1B

(01rpm-99999rpm) is used to calibrate the rotation of

the tool electrode RPM on speed controller

S.

No.

Name of parts Specification

1. PMDC Motor 0.25hp, 1500 RPM

2. Variac 0.5 hp DC drive

3. V-belt M 6x500

4. Diameter of driving

& driven pulleys

60 mm

5.

Bearing housing Outer diameter 50 mm

and inner diameter 45

mm, mild steel

6. Bearing Antifriction ball

bearing

7. Shaft 13 mm diameter, mild

steel

8. Thickness of Al-

alloy base plate

12 mm

9. Electrode holder 8.5 mm diameter

V

Grinding

wheel

Bearing

housing

Driven

pulley

Spindle

DC Motor

All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12

power transmitted from electrical motor to spindle

through driver pulley mounted on motor shaft and

‘V’ belt of trapezoidal section.

Table 1 Specifications of different parts

The rotating spindle is supported on four

ball bearings in housing, so that axial thrust

the axial movement

The selection of these four

ball bearings is done based on the expected

and endurance run.

Schematic diagram of EDDFG attachment

Dimensional specification of ‘V’ belt is M6x500.

avoid slippage. The

alloy plate fitted on

tachometer Electronic Automation

Private Ltd (EAPL), India make model: DT 200 1B

99999rpm) is used to calibrate the rotation of

on speed controller (variac).

Figure 3 EDDFG attachment fitted on

EDM Machine

3 Fabrication of MMC

Aluminium ingots are melted in a graphite crucible

of a tilting oil-fired furnace at a temperature of about

800oC. Diesel was used as the fuel in oil

Figure 4 Melting of Aluminium alloy

The melting of the Al6061 alloy at th

temperature and is being kept for more than 2 hrs 45

min. A controlled atmosphere has been maintained

inside the furnace to prevent oxidation of the molten

metal by using cap of oil-fired furnace. At the same

time the reinforcing SiC particulate (6

10% by weight fraction was pre

approximately 45 minute to remove surface impurities

and assist in the adsorption of gases. The preheated SiC

particles continuously entered in to the molten metal via

a long handle spoon with small amount at a time along

with continuously stirring manually with a mild steel

rod about 20 to 30 min. The flame intensity of oil

furnace was regulated accordingly to the requirement

via blower. The composite mixture has been collected

from the crucible to a ladle and then is poured in the

sand mould. It passes through the runner system and

enters into the cavity and settles down. The composite

Specification

, 1500 RPM

DC drive

x500

Outer diameter 50 mm

and inner diameter 45

mm, mild steel

Antifriction ball

bearing

13 mm diameter, mild

8.5 mm diameter

Driving

pulley

Al base plate

V- belt

All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT

564-3

Figure 3 EDDFG attachment fitted on

achine

Aluminium ingots are melted in a graphite crucible

fired furnace at a temperature of about

C. Diesel was used as the fuel in oil-fired furnace.

luminium alloy

6061 alloy at the preset

is being kept for more than 2 hrs 45

controlled atmosphere has been maintained

inside the furnace to prevent oxidation of the molten

fired furnace. At the same

time the reinforcing SiC particulate (600 mesh number)

10% by weight fraction was pre-heated for

approximately 45 minute to remove surface impurities

and assist in the adsorption of gases. The preheated SiC

particles continuously entered in to the molten metal via

amount at a time along

with continuously stirring manually with a mild steel

rod about 20 to 30 min. The flame intensity of oil-fired

furnace was regulated accordingly to the requirement

via blower. The composite mixture has been collected

le to a ladle and then is poured in the

sand mould. It passes through the runner system and

enters into the cavity and settles down. The composite

DEVELOPMENT AND EXPERIMENTAL INVESTIGATION OF ELECTRO-DISCHARGE DIAMOND FACE GRINDING

564-4

mixture was allowed to solidify for approximately 1hr

and finally the mould is broken to get the desired

casting component.

Figure 5 Manual stirring view of oil-fired

furnace at the time of fabrication of MMC Al/SiCp

The casted metal matrix composite was machined

to get the cylindrical shape. The pictorial views

manufactured metal matrix composite are shown in

figure given below.

(a) (b)

Figure 6(a) MMC workpieces of disc shape

(b) EDDFG wheel

Table 2 Specifications of grinding wheel

Abrasive Diamond

Concentration 75 %

Grit number 80/100

Grade M (Medium)

Bonding Material Bronze

Depth of abrasive 10 mm

Wheel diameter 30 mm

Holding length 40 mm

Holding diameter 8.3 mm

4 Experimentation

EDDFG process is performed on the workpiece

specimens in reverse polarity on Smart ZNC EDM

machine. During EDDFG process, rotating wheel

electrode moves downwardsunder servo control

mechanism and maintains inter electrode gap (IEG).

IEG depends upon breakdown strength of dielectric

fluid. Both wheel electrode and workpiece are

submerged in dielectric fluid. The variac was connected

in-line with PMDC motor used to control wheel RPM.

Workpeicespecimens wereheld in vice and leveled

horizontal with help of spirit level. After an exhaustive

pilot experimentationinput process parameter ranges are

determined. The input process parameters are gap

current, pulse on-time, duty factor, wheel RPM. On the

basis of pilot experimentation it was decided to conduct

the experiments in reverse polarity withconstant pulse

off time of 40 µs. The variation in Ra and MRR were

observed by varyingone input process parameter at a

time, keeping other parameters constant.The Ra value

was measured using a Surface Roughness Tester with

accuracy of 0.01µm (SURTRONIC-25 model, Taylor

Hobson Ltd.) and for evaluation of MRR, the loss in

weight of the machined specimen was measured on a

weighing digital microbalance (accuracy 10 µg, CAS

India Private Limited)

5 Results and Discussion

Influences of wheel rotation, gap current and pulse

on-time on the material removal rate (MRR) and

average surface roughness (Ra) are investigated.

5.1 Effect of wheel RPM

The effect of wheel speed on Ra is shown in fig. 7,

for different values of gap current keepingconstant pulse

on-time at 40 µs and pulse off-time at 40µs. Ra value

slightly increases on increasing wheel RPM due to

corresponding increase in flushing action and diamond

abrasive grinding.

Figure 7 Effect of wheel RPM on Raat different

current values (pulse on-time 40µs & off-time 40µs)

The effect of wheel RPM on MRR is shown in fig. 8,

for different values of gap current keepingconstant pulse

on-time at 140 µs and pulse off-time at 40µs. MRR

increases on increasing wheel RPM because of

corresponding increase in flushing action and abrasion

action by diamond abrasives.

500 600 700 800 900 1000 1100 1200 13003

3.71

4.42

5.13

5.84

6.55

7.26

7.978Effect of rotating grinding wheel on Average Roughness for different current at on time 40 µs %

Wheel RPM

Surface R

oughness (R

a)

4 A

6 A

8 A

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT

Guwahati, Assam, India

564-5

Figure 8 Effect of wheel RPM on MRR at different

current values (Pulse on-time 140µs & off-time 40µs)

5.2 Effect of Gap current

The effect of gap current on Ra and MRR are

shown in fig. 9 and fig. 10, for different values of pulse

on-timekeepingconstant wheel RPMand pulse off-time

at 40µs.

Figure 9 Effect of gap current on Ra at different

pulse on-time (wheel RPM 600 and off-time 40µs)

Figure 10 Effect of gap current on MRR at different

pulse on-time (wheel RPM 1200 and off-time 40µs)

On increasing gap current results increase in spark

energy which increases melting and evaporation of

work material causes larger crater depth subsequently

results an increase in Ra and MRR. Larger crater depth

is responsible for increase in Ra and increase in spark

energy results rise of MRR.

5.3 Effect of Pulse on-time

The effect of pulse on-time on Ra is shown in fig.

11, for different values of pulse on-timekeeping

constant gap current at 4A and pulse off-time at 40

µs.Ra value increases on increasing pulse on-time

because of corresponding increase in duration of heat

addition resultingincreased spark energy. Increased

spark energy causes increase recast layers at machined

surface and gives poor surface finish.

Figure 11 Effect of pulse on-time on Ra at different

wheel RPM (gap current 4 A and off-time 40µs)

More heat addition in each spark makes ease of

material removal by electro erosion and abrasion action

result corresponding increase in MRR as shown in fig.

12. MRR increases with increasing pulse on-time at

different wheel RPM keeping constant gap current at 8A

and pulse off-time at 40µs.

Figure12 Effect of pulse on-time on MRR at different

wheel RPM (gap current 8A & off-time 40µs)

6 Analyses of SEM Micrographs

Irregular surface texture is rectified upto some

extent as shown in figure 13 (b)but presence of recast

layers on machined surface as a result of higher pulse

on-time andthe scratches due to diamond abrasives are

notappeared on machined surface as a result of larger

spark size.

500 600 700 800 900 1000 1100 1200 13000.005

0.0098

0.0146

0.0194

0.0242

0.029

0.0338

0.0386

0.04

Wheel RPM

MR

R (gm

/min

)

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.53

3.71

4.42

5.13

5.84

6.55

7.26

7.978

Gap current (A)

Surface R

oughness (R

a)

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.50.005

0.0087

0.0124

0.0161

0.0198

0.0235

0.0272

0.0309

0.0346

0.0383

0.04

Gap current (A)

MR

R (gm

/min

)

40 60 80 100 120 1403.25

3.71

4.17

4.63

5.09

5.55

6Effect of duty factor on Average Roughness for different rpm at 4 A

Pulse on-time (µs)S

urface roughness (R

a)

40 60 80 100 120 1400.015

0.0168

0.0185

0.0203

0.022

0.0238

0.0255

0.0273

0.029

0.0308

0.0325

0.0343

0.036

0.0378

0.03950.04

Pulse on-time (µs)

MR

R (gm

/min

)

4 A

6 A

8 A

600 RPM

1200 RPM

900 RPM

40 µs

90 µs

140µs

40 µs

90 µs

140µs

600 RPM

1200 RPM

900 RPM

DEVELOPMENT AND EXPERIMENTAL INVESTIGATION OF ELECTRO-DISCHARGE DIAMOND FACE GRINDING

564-6

Figure 13 (a) before machining (b) after machining

Diamond abrasives assisted quick removal of SiC

particles results minimized cavity due to electro erosion

for removal SiCp particle.

7 Conclusions

1. Metal matrix composite of Aluminium Silicon

Carbide (Al-SiCp) improves the material properties

like strength to weight ratio, heat resistance, wear

resistance, hardness etc. and can be easily machined

on EDM machine with better productivity.

2. Machining of Al-SiCpmetal matrix composite with

the combination of Electro-Discharge Grinding and

Diamond Grinding improves the grinding

performance more than the sum of individual

machining performance.

3. Electro-Discharge Diamond Face Grinding process

experimented on Al-SiCpcomposite, indicates MRR

increases with increase in wheel speed for all

values of current within the specified range.

4. The average surface roughness (Ra) increase with

increase of wheel speed for all values of gap

current.

5. The effect of wheel speed on MRR is more

significant than that for Ra value. MRR increases on

increasing wheel RPM because of corresponding

increase in flushing action and diamond abrasive

grinding.

6. Presence of recast layers on machined surface as a

result of higher pulse on-time and the scratches due

to the diamond abrasives are not appeared as result

of larger spark size. Diamond abrasives assisted

quick removal of SiC particles results minimized

cavity due to electro erosion for removal of SiC

particles.

References

Abothula B. C., Yadava V. and Singh G. K. (2010),

Development and Experimental Study of Electro-

Discharge Face Grinding, Materials and Manufacturing

Processes, Vol. 25, pp.1-6.

Choudhary S. K., Jain V. K. and Gupta M. (1999),

Electric-Discharge of Diamond Grinding of High Speed

Steel, Machining Science and Technology, Vol. 3(1),

pp.91-105.

Grodzinskii E. Ya. (1979), Grinding with Electrical

Activation of the Wheel Surface, Machines Tooling,

Vol. 50, pp.10-13.

GrodzinskiiEYa. andZubotava L. S. (1982),

Electrochemical and electrical-discharge abrasive

machining, Soy. Engng Res., Vol. 2, (3), pp.90.

Koshy P., Jain V. K. and Lal. G. K. (1996), Mechanism

of Material Removal in Electrical Discharge Diamond

Grinding, International Journal of Machine Tools and

Manufacture, Vol. 36(10), pp.1173-1185.

Mohan B., Rajadurai A. and Satyaanarayana K. G.

(2002), Effect of SiC and rotation of electrode on

electric discharge machining of Al-SiC composite,

Journal of Material Processing Technology Vol. 124,

pp.297-304.

Ramesh K. C. and Sagar R. (1999), Fabrication of Metal

Matrix Composite Automotive Parts, International

Journal of Advanced Manufacturing Technology, Vol.

15, pp.114–118.

Singh G. K., Yadava Vinod and Kumar R. (2010),

Diamond face grinding of WC-Co composite with spark

assistance: Experimental study and parameter

optimization, International Journal of Precision

Engineering and Manufacturing, Vol. 11 (4), pp. 509-

518.

Singh G. K., Yadava Vinod and Kumar R. (2011),

Experimental study and parameter optimization of

electro-discharge diamond face grinding, International

Journal of Abrasive Technology, Vol. 4, No. 1.

Velmurugan C., Subramanian R., Thirugnanam S. and

Ananadavel B. (2011), Experimental Investigation on

Machining Characteristics of Al6061 Hybrid Metal

Matrix Composites Processed by Electrical Discharge

Machining, International Journal of Engineering

Science and Technology, Vol. 3 (8), pp.87-101.

Vitlin V. B. (1981), Model of the Electro-Contact-

Abrasive Cutting Process, Soviet Engineering Research,

Vol. 1, pp.88-91.

YadavSanjeev Kumar Singh, Yadava Vinod&Narayana

V. Lakshmi (2008), Experimental Study and Parameter

Design of Electro-Discharge Diamond Grinding,

International Journal of Advanced Manufacturing

Technology, Vol. 36, pp.34–42.