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
Experimental Evaluations on Surface Quality Improvement in Aluminium
Powder Mixed AEDM of Nickel Based Super Alloy 718 with Cryogenically
Treated Copper Electrode
Anil Kumar*, Naveen Beri, Harish Pungotra
Department of Mechanical Engineering, Beant College of Engineering and Technology, Gurdaspur, Punjab,
*Corresponding Author E-mail ID: ak_101968@yahoo.com
Abstract
In this experimental study attempt has been made to realize potential in enhancing surface quality with fine
aluminum additives powders in AEDM of nickel based super alloy Inconel 718. L 36 Orthogonal Array has been
selected to conduct and analyze experiments based on Taguchi methodology. Peak current, pulse on time, duty
cycle, gap voltage, retract distance, concentration of fine aluminum powder added into the dielectric fluid are
chosen as input process variables to study performance in terms of surface roughness using copper and deep
cryogenically treated copper electrode. It is observed that addition of 6g/l of fine aluminium powder and
cryogenically treated copper electrode improves the surface finish appreciably. The recommended best
parametric settings for minimum surface roughness have been verified by conducting confirmation experiments.
Keywords: AEDM, Taguchi methodology, Orthogonal Array, cryogenic treatment, surface roughness.
1. Introduction
Today’s manufacturing industry is facing challenges like difficulty in machining of advance extra hard and tough
materials (super alloys, ceramics, and composites), stringent design requirements (high precision, complex
shapes and high surface quality) and machining costs. The greatly-improved thermal, chemical, and mechanical
properties of the material such as improved strength, heat resistance, wear resistance, and corrosion resistance,
while having yielded enormous economic benefits to manufacturing industries through improved product
performance and product design, are making traditional machining processes unable to machine them or unable
to machine them economically. EDM has proven to be applicable to all electrically conductive materials
regardless of their physical and metallurgical properties. In EDM, material removal is achieved by preferential
erosion of the work piece electrode as controlled discrete discharges are passed between the electrode and the
work piece in dielectric medium. EDM is a widespread technique used in industry for high precision machining
of all types of conductive materials such as: metals, metallic alloys, graphite or even some ceramic materials and
super alloys such as Inconel, of any hardness [1]. Since the invention of EDM in 1940s researchers have made a
lot of efforts to improve the machining performance. A number of variants have emerged to manifolds the
application of EDM process in industry. In traditional EDM process surface roughness is more and material
removal rate is relatively less. To fulfill the objectives of improving manufacturing efficiency and quality of
shaping and finishing processes researchers have taken many directions. A relatively new advancement in this
direction is to use some additives powders suspended in the dielectric fluid of EDM to fulfill the requirement of
minimum surface damage, enhance machining rates and improving surface properties. This new hybrid
machining process is called additive mixed electrical discharge machining [2-5].
The machining mechanism of AEDM is different from conventional EDM process [6-7]. In AEDM when a
voltage of 80-320V is applied across work piece and electrode electrical intensity in the range of 10 5 to 10 7 V/m
is generated. Under the influence this electric intensity additives powder particles get energized and behave in a
zigzag fashion. These additives particles arrange themselves in the form of chain at different places under the
sparking area leading to bridge formation. This bridging effect promotes early explosion in the gap. As a result,
the series discharge starts under the electrode area. Due to increase in frequency of discharging, faster erosion
takes place from the work piece surface. Therefore gap contamination with fine abrasive conductive particles
facilitates ignition process and increases maching rates and due to better distribution of spark energy resulting in
improved surface roughness. Process performance of AEDM depends upon electrical parameters (like pulse
frequency, duty cycle, pulse on time, spark gap, current, and voltage), material properties of electrode, work
piece and dielectric fluid, and properties of abrasive powders (like melting point, specific heat, thermal
conductivity, grain size, and concentration). Therefore, promoting the process performance by developing a
thorough understanding of the relationship between these parameters has become a major research concern [8-
11].
Erden and Belgin [12] were the first who studied the effect of impurities (copper, aluminium, iron and carbon) in
electrical discharge machining of brass steel and copper steel pair and reported increase in machining rates with
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