Investigation on Electrochemical Discharge Machining of Fibre Composites

I. Gomes, B.R. Sarkar, Dr. B. Doloi & Dr. B. Bhattacharyya

Production Engineering Department Jadavpur University

Kolkata-700032

INTRODUCTION

Composite materials are gaining wide acceptance in applications where high specific strength, good elevated temperature properties and good wear resistance.

Conventional cutting of composite has certain problems like surface roughness, cutting of fibers.

In case of drilling, reports of damage at the entrance and exit wall of holes exist .

Unconventional machining is an alternative to machining of composites.

Electrochemical discharge machining is a new and developing hybrid method of machining of composites.

Effective utilisation of such process holds the promises of good surface finish, effective material removal rate and accuracy.

The fundamental material removing process in ECDM is by combined effect of electrochemical and electrical spark discharge action .

The basic characteristic of material removal in ECDM is based on the utilization of energy released by sparking which raises the temperature of the work piece.

Fractured related spalling may also help in material removal rate.

To perform through hole drilling on GFRP composites using Electrochemical Discharge Machining (ECDM) process.

To study the effects of various process parameters on different machining performances.

OBJECTIVES

EXPERIMENTAL PLANNING

The ECDM set up has various sub-systems such as pulsed D.C. power supply, a work piece holding arrangement, a tool mounting unit, a gravity feeding arrangement and a machining chamber.

A set of through hole was drilled on glass fibre reinforced plastics (GFRP) work-sample procured commercially.

Fig.1. Schematic diagram of experimental ECDM set-up for drilling

GFRP composites or Glass Fibre Reinforced Plastics are the most commonly used in mechanical joints in pipes and structures in industry, military defence, marine and offshore application.

Sodium hydroxide (NaOH) salt was used as the electrolyte. Voltages were set at 35V, 45V and 55V. Electrolyte concentrations were 10%, 20% and 30% by weight. Inter-electrode gap were fixed at 20mm, 30mm, 40mm. Machining time was noted until a through hole was produced and recorded

with the help of a stopwatch. The amount of work and tool material removal were measured by taking

the difference in weight of the specimen before and after machining with the help of Mettler Toledo balance of LC 1×10-5gm.

RESULTS AND DISUSSIONS

Expt. Voltage Concentration IEG

M/Cing Time MRR TWR

No. (volt) (wt.%) (mm) (min) (mg/min) (mg/min)

1 35 20 30 65 0.049 0.00044

2 45 20 30 70 0.424 0.00143

3 55 20 30 20 0.446 0.0046

4 45 10 30 21 0.128 0.00017

5 45 20 30 70 0.424 0.00143

6 45 30 30 35 0.295 0.00033

7 45 20 20 30 0.431 0.007

8 45 20 30 70 0.424 0.00143

9 45 20 40 30 0.01 0.0178

Table 1: Experimental Results

MRR = (Weight of W/P before M/Cing - Weight of W/P after M/Cing)Time of M/Cing

TWR = (Weight of Tool before M/Cing - Weight of Tool after M/Cing)Time of M/Cing

PARAMETRIC INFLUENCES ON MATERIAL REMOVAL RATE

Voltage 45 V, IEG 30mm

0

0.1

0.2

0.3

0.4

0.5

10 20 30Concentration of electrolyte( wt%)

MR

R (

mg

/min

)

Electrolyte concentration 20%, IEG 30mm

0

0.2

0.4

0.6

35 45 55Applied voltage( volt)

MR

R (

mg

/min

)

Fig. 2. Effect of Applied voltages on MRR

Fig. 3. Effect of Electrolytic concentration on MRR

Electrolyte concentration 20%, voltage 45 V

0

0.1

0.2

0.3

0.4

0.5

20 30 40Inter-electrode gap (mm)

MR

R (

mg/m

in)

Fig. 4. Effect of Inter-electrode gap on MRR

PARAMETRIC INFLUENCES ON TOOL WEAR RATE

Voltage 45 V, IEG 30 mm

0

0.0004

0.0008

0.0012

0.0016

10 20 30Electrolyte concentration (wt%)

TW

R (

mg

/min

)

Electrolyte concentration 20%, IEG 30 mm

0

0.002

0.004

0.006

35 45 55Applied voltage (volt)

TW

R (

mg

/min

)

Fig. 5. Effect of Applied voltage on TWR Fig. 6. Effect of Electrolyte concentration on TWR

Electrolyte concentration 20%, voltage 45 V

0

0.002

0.004

0.006

0.008

20 30 40Inter-electrode gap (mm)

TW

R (

mg

/min

)

Fig. 7. Effect of inter-electrode gap on TWR

Fig. 8. GFRP machined at 45V/ 20wt% / 30mm

Fig. 9. GFRP machined at 45V/ 20wt% / 30mm

Fig. 10. GFRP machined at 55V/ 20wt% / 30mm

ANALYSIS BASED ON PHOTOGRAPHS

Fig. 11. GFRP machined at 55V/ 20wt%/ 30mm

Fig. 12. GFRP machined at 45V/ 10wt% / 30mm

Fig. 13. GFRP machined at 45V/ 10wt% / 30mm

CONCLUSION

ECDM process can effectively be utilized against machining of glass fibre reinforced composite.

an optimum voltage, concentration of electrolyte and inter electrode gap exist, which leads to optimum material removal rate which is at 55V, 20% and 20mm.

Deposition on tool during the machining process takes place due to electrochemical reactions.

High level of electrolyte results in heat-affected zone formation and damages the work-sample.