OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
AF 5 and Poco EDM I in EDM of seal slots in a jet engine turbine vane. MRR in case EDM - I was higher than
Poco AF 5. Ghewade and Nipanikar, (2011) has been reported the machining of Inconel 718 using WEDM with
a copper electrode. The Taguchi method is used to analysis the significance effect of each parameter i.e. peak
current , gap voltage , duty cycle and pulse on time an machining characteristics such Material Removal Rate
,Electrode wear rate and Radial over cut and half taper angle .Peak current significantly affect the Material
Removal Rate and pulse on time significantly affect the Electrode wear rate. Liu et al., (2005) present a process
using micro electro discharge machining combined with high frequency dither grinding to improve the surface
roughness of micro hole machining of high Nickel alloy. This technique eliminate the micro cracks along with
reduce surface roughness from 2.12 to 0.85 µm Rmax. Liu et al., (2006) investigated the significant machine
parameters which are affecting the characteristics of micro holes in high Nickel alloy in terms of micro hole
expansion, electrode depletion and material removal rate. A proper discharge current is very important to achieve
optimum results.
Hewidy et al.,(2005) correlated the various WEDM parameters such as peak current, duty factor, wire tension,
and water pressure with the performance outputs namely metal removal rate (MRR), wear ratio and surface
roughness in WEDM of Inconel 601. Aspinwall et al., (2008) presents roughing and finishing strategies of Ti-
6Al-4V and Inconel 718 after WEDM. The average recast layer thickness less than 11 µm is to be found and
several trim passes showing no apparent recast. There is no significant change in work piece microhardness.
Kumar et al. investigated the optimum WEDM process parameters’ of Incoloy 800 super alloy with multiple
machining performance characteristics such as material removal rate , surface roughness and kerf by using Gray
– Taguchi method.
Nimonic 90 is a newly developed Nickel based heat resistance super alloy with high content of Cobalt and
Chromium. Processing of such type of heat resistance alloys has been an active area of research due to increasing
demand of this class of material and typical problems associated with the processing. Machining of heat
resistance alloys is difficult due to a combination of low thermal conductivity and high temperature strength. It is
very difficult to machine Nimonic 90 by conventional machining processes. Modern machine techniques such
WEDM are increasingly being used for machine such hard material. Hence, this study focused on machining of
Nimonic 90 using WEDM in order to fulfill the production and quality requirement. In present work, influence
of WEDM parameters namely discharge current, pulse-on time, pulse-off time, servo voltage and wire feed rate
have been evaluated on machinability of Nimonic-90. Cutting speed is considered as machinability attribute.
2. Experimental Procedure
The machining experiments were performed on 5 axis sprint cut (ELPUSE-40) wire EDM manufactured by
Electronic M/C Tool LTD India.
In present machine tool ,parameters can be varied under following range; discharge current (Ip), 10-230 amp;
pulse on time (Ton) ,101-131 μs; pulse off time (Toff) ,10-63 μs ; servo voltage (SV), 0-90 V; dielectric flow
rate (DFR) , 0-12 liter per minute ; wire feed rate(WF) ,1-15 m/min; wire tension (WT) ,1-15 N. Copper coated
brass wire of diameter 0.25mm was used as an electrode because of its good capability to sustain high discharge
energy. Distilled water was used as a dielectric fluid with conductivity 20 S.
Nimonic-90, a nickel based super-alloy having 60% Ni, 19.3% Cr, 15% Co, 3.1% Ti, 1.4% Al, was taken as a
work material in the form of a rectangular sheet of 22.5 mm thickness. The density and melting point of
Nimonic-90 was measured as 8.18 g/cm 3 and 1370 0 C respectively.
Cutting speed was measured as machinability attribute for Nimonic-90, which was observed directly from
monitor screen of the machine tool. Single machining variable is varied at a time to study the influence of
discharge current (Ip), pulse on time (Ton), pulse off time (Toff), servo voltage (SV) and wire feed on cutting
speed (CS).
3. Effect of WEDM parameters on cutting speed
3.1. Effect of discharge current
The effect of discharge current on cutting speed of Nimonic 90 with wire EDM is shown in Figure 1 and 2 under
the two different setting of pulse on time (108-120μs ) along with two different setting of pulse off time (35μs
and 45μs). The other parameters were fixed such as Servo voltage 20V, Wire tension 10N, Wire feed 5
meters/min., servo feed 2080 and dielectric flow rate 10 liter per min (upper and lower nozzles).
It is clear from the fig. 1 at low pulse duration (Ton =108µs), the cutting speed is increase slowly with increase
of peak current. But at high pulse duration (Ton =120μs) there is sharply increase of cutting speed with increase
of peak current from 40A to 80 A. Increase in the peak current leads to increase in the rate of the heat energy and
hence in the rate of melting and evaporation.
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