Investigation on ElectrochemicalDischarge Machining of FibreCompositesI. Gomes, B.R. Sarkar, Dr. B. Doloi & Dr. B. BhattacharyyaProduction Engineering DepartmentJadavpur UniversityKolkata-700032
INTRODUCTION Composite materials are gaining wide acceptance in applicationswhere high specific strength, good elevated temperature properties andgood wear resistance. Conventional cutting of composite has certain problems like surfaceroughness, cutting of fibers. In case of drilling, reports of damage at the entrance and exit wall ofholes exist . Unconventional machining is an alternative to machining ofcomposites. Electrochemical discharge machining is a new and developing hybridmethod of machining of composites. Effective utilisation of such process holds the promises of goodsurface finish, effective material removal rate and accuracy.
The fundamental material removing process in ECDM is by combinedeffect of electrochemical and electrical spark discharge action . The basic characteristic of material removal in ECDM is based on theutilization of energy released by sparking which raises the temperature ofthe work piece. Fractured related spalling may also help in material removal rate.
To perform through hole drilling on GFRP composites usingElectrochemical Discharge Machining (ECDM) process. To study the effects of various process parameters on differentmachining performances.OBJECTIVES
EXPERIMENTAL PLANNING The ECDM set up has varioussub-systems such as pulsedD.C. power supply, a workpiece holding arrangement, atool mounting unit, a gravityfeeding arrangement and amachining chamber. A set of through hole wasdrilled on glass fibre reinforcedplastics (GFRP) work-sampleprocured commercially.Fig.1. Schematic diagram ofexperimental ECDM set-up for drilling
GFRP composites or Glass Fibre Reinforced Plastics are the mostcommonly 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 recordedwith the help of a stopwatch. The amount of work and tool material removal were measured by takingthe difference in weight of the specimen before and after machining withthe help of Mettler Toledo balance of LC 1×10-5gm.
RESULTS AND DISUSSIONSExpt. Voltage Concentration IEGM/CingTime MRR TWRNo. (volt) (wt.%) (mm) (min) (mg/min) (mg/min)1 35 20 30 65 0.049 0.000442 45 20 30 70 0.424 0.001433 55 20 30 20 0.446 0.00464 45 10 30 21 0.128 0.000175 45 20 30 70 0.424 0.001436 45 30 30 35 0.295 0.000337 45 20 20 30 0.431 0.0078 45 20 30 70 0.424 0.001439 45 20 40 30 0.01 0.0178Table 1: Experimental ResultsMRR = (Weight of W/P before M/Cing - Weight of W/P after M/Cing)Time of M/CingTWR = (Weight of Tool before M/Cing - Weight of Tool after M/Cing)Time of M/Cing
PARAMETRIC INFLUENCES ON MATERIALREMOVAL RATEVoltage 45 V, IEG 30mm00.10.20.30.40.510 20 30Concentration of electrolyte( wt%)MRR(mg/min)Electrolyte concentration 20%, IEG 30mm00.20.40.635 45 55Applied voltage( volt)MRR(mg/min)Fig. 2. Effect of Applied voltages on MRR Fig. 3. Effect of Electrolytic concentrationon MRRElectrolyte concentration 20%, voltage 45 V00.10.20.30.40.520 30 40Inter-electrode gap (mm)MRR(mg/min)Fig. 4. Effect of Inter-electrode gap on MRR
PARAMETRIC INFLUENCES ON TOOL WEAR RATEVoltage 45 V, IEG 30 mm00.00040.00080.00120.001610 20 30Electrolyte concentration (wt%)TWR(mg/min)Electro lyte co ncentratio n 20%, IEG 30 mm00.0020.0040.00635 45 55Applied voltage (volt)TWR(mg/min)Fig. 5. Effect of Applied voltage on TWR Fig. 6. Effect of Electrolyte concentrationon TWRElectrolyte concentration 20%, voltage 45 V00.0020.0040.0060.00820 30 40Inter-electrode gap (mm)TWR(mg/min)Fig. 7. Effect of inter-electrode gap on TWR
CONCLUSION ECDM process can effectively be utilized against machining of glassfibre reinforced composite. an optimum voltage, concentration of electrolyte and inter electrodegap exist, which leads to optimum material removal rate which is at55V, 20% and 20mm. Deposition on tool during the machining process takes place due toelectrochemical reactions. High level of electrolyte results in heat-affected zone formation anddamages the work-sample.