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
MODELLING FOR MACHINING SPEED IN WEDM OF WC-5.3%CO
COMPOSITE USING RESPONSE SURFACE METHODOLOGY
Kamal Jangra 1* and Sandeep Grover 2
1 Asst Professor,Department of Mechanical Engineering, YMCA UST, Faridabad, India-121006.
2 Professor ,Department of Mechanical Engineering, YMCA UST,Faridabad, India-121006
1* E-mail: kamaljangra84@gmail.com
Abstract
Wire electrical discharge machining (WEDM) is a well known process for machining hard metal alloys and
metal matrix composites. In this paper, four important WEDM parameters namely pulse-on time, pulse-off time,
servo voltage and wire feed rate have been investigated and modelled for machining speed of WC-5.3%Co
composite during rough cutting operation on WEDM. Using response surface methodology, face centered central
composite design has been adopted to perform the experiments. Achieving higher machining speed is the main
objective of rough cutting operation. Therefore, using desirability function, parameters have been predicted for
maximizing the machining speed.
Keywords: WEDM, Tungsten carbide, Machining speed, Response surface methodology
1. Introduction
Tungsten carbide (WC-Co) composite is a powder metallurgy product which posses’ high hardness even at
elevated temperatures which makes it suitable for dies and tool industries. Because of high hardness (70-90
HRC) and melting point ˃2800 (
0 C) (Scussel, 1992), tungsten carbide composite is difficult to machine with
conventional manufacturing processes. Wire electrical discharge machining (WEDM) is a special form of
electrical discharge machining (EDM) which has the capability to produce intricate shapes and profiles in hard
metal alloys and metal matrix composites, with high degree of accuracy, without making any mechanical contact
(Jangra et al. 2010). In WEDM, surface material is eroded by melting or evaporation due to large amount of heat
generated between the work material and downward moving wire electrode as shown in Figure 1.
Figure 1 Schematic Representation of WEDM
In WEDM, achieving higher machining speed or material removal rate is prime objective during rough
cutting operation. However, due to large number of parameters and their wide varying range in WEDM,
prediction of optimal machining parameters is difficult. In order to achieve an efficient process planning in
machining of WC-Co composite into desired shape, need of accurate machinability data arises. Jangra et al.
(2011a) evaluated the effect of various factors and their sub-factors on machinability of WC-Co composite with
WEDM using digraph and matrix method. They broadly grouped these factors into work material, machine tool,
tool electrode, cutting conditions and geometry to be machined. Machinability was measured in terms of material
removal rate (MRR). They concluded that the machine tool is the most influencing factor affecting the
machinability of WC-Co composite. Influence of composition and grain size of WC-based cermets on
machinability by WEDM has been studied by Lauwers et al. (2006). It was shown that the cutting rate decreases
with increasing grain size and cobalt percentage, which can be explained mainly by the change in thermal
conductivity of the material. Jangra et al., (2011b) investigated the effect of peak current, pulse on time, pulse-
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