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
off time, servo voltage, dielectric flow rate, wire feed rate, wire tension and taper angle on machinability of
tungsten carbide composite with WEDM.
According to Garg et al., (2010), most of the available literatures on machinability of WC-Co composite
deals with die sinking EDM (Mahdavinejad, 2005; Kanagrajan et al., 2008; Kung et al., 2009) and more work yet
to be tried on WEDM. Therefore, in present work, four important WEDM parameters have been investigated and
modelled for predicting the machining speed of WC-5.3%Co composite on WEDM.
2. Experimentation
In present work, experiments were performed on 5-axis sprint cut (ELPLUS-40) WEDM manufactured by
Electronic Machine Tool Ltd, India. The range of variable parameters in present machine tool are as follows:
discharge current, 10-230 ampere; pulse-on time, 100-131machine unit (mu); pulse-off time,14-63mu; wire
speed, 1-15 m/min.; wire tension, 1-15N; servo voltage, 10-90V; dielectric flow rate 0-12 litre per minute
Tungsten carbide composite having low cobalt concentration (5.3%) has been taken as a work material in the
form of rectangular block of thickness 13mm. The density and hardness of WC-5.3%Co composite was
measured as 14.95g/cm 3 and 77 HRC respectively. Machining speed (MS) was measured as surface area
removed per minute (mm 2 /min). It was obtained by multiplying the workpiece thickness (13mm) with linear
cutting speed (mm/min) displaying on machine tool monitor screen.
Four variables namely pulse-on time, pulse-off time, servo voltage and wire feed rate have been considered.
Discharge current was kept at optimum value of 90amp which has been taken on the basis of preliminary
experiments (Jangra et al., 2011). Dielectric flow rate was kept at 12LM -1 . High flow rate results in quick and
complete flushing of melted debris out of the spark gap. Zinc coated brass wire of diameter 0.25mm was used as
an electrode because of its good capability to sustain high discharge energy. Vertical cutting was performed at
zero wire offset. Wire tension was fixed at 10N.
Table 1 Process parameters and their levels
Symbol Parameters Units Levels
(-1) (0) (+1)
A Pulse-on time (Ton) Machine unit (mu) 108 115 122
B Pulse-off time (Toff) Machine unit (mu) 30 40 50
C Servo Voltage (SV) Volt 20 30 40
D Wire Feed rate (WF) m/min. 4 6 8
Based upon the input factors and their levels as listed in Table 1, the experimental plan was designed on the
basis of standard RSM design called face centered Central Composite Design (CCD). This design consists of
factorial portion with all factors at three levels, eight star points and six central points. The star points are at the
face of the cube portion on the design which corresponds to α value of 1. The centre points, as implied by the
name, are points with all levels set to coded level 0, the midpoint of each factor range. Table 2 shows the
experimental layout and results obtained for machining speed.
Normal Plot of Residuals
99
Normal % Probability
95
90
80
70
50
30
20
10
5
1
-3.00 -2.00 -1.00 0.00 1.00 2.00 3.00
Internally Studentized Residuals
Figure 2 Normal probability plot of residuals for MS
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