Journal of Engineering Science and Technology (Sep 2017)
GREY RELATIONAL ANALYSIS AND ITS APPLICATION ON SURFACE PROPERTIES DURING EDM AND POWDER MIXED EDM
Abstract
Electrical discharge machining is an extensively used non-conventional process for material removal in die manufacturing and aerospace industries. The mechanism of powder mixed electric discharge machining is very different from that of electrical discharge machining process. It was found that considerable research has been done on different aspects during electric discharge machining of various steels, but sufficient data is not available on the surface properties and optimum process parameters for machining of H-11 die steel. The present work investigates the effect of process parameters like powder oncentration, peak current, pulse-on-time, duty cycle and gap voltage on material removal rate, surface roughness, recast layer thickness and microhardness simultaneously during electrical discharge machining and powder mixed electrical discharge machining of H-11 hot work tool steel. Multiobjective optimization using grey relational analysis was used to determine the optimal setting of process parameters for maximum material removal rate, minimum surface roughness, minimum recast layer thickness and maximum micro-hardness simultaneously. The work material has been selected due to its brilliant mechanical properties and diverse industrial applications. Taguchi’s L27 orthogonal array was used to carry out the experiments. Analysis of variance was performed to determine the significant parameters at a 95% confidence interval. Conductive powder mixed to the dielectric fluid was graphite of size less than 53µm obtained from the sieve analysis. Electrolytic copper was used as the tool electrode. Investigation of micro-structures was done using scanning electron microscope to examine alterations and defects on the machined surface. Grey relational analysis exhibits an improvement of 0.2025 in the grey relational grade. The tendency of deviation of the response curves suggest that powder concentration of 0g/l, peak current of 3A, pulse-ontime of 150µs, duty cycle of 70% and gap voltage of 30V offer maximum grey relational grade when machined during electrical discharge machining and graphite powder mixed electrical discharge machining. The surface properties during powder mixed electrical discharge machining using graphite powder do not show much improvement in comparison to machining without addition of powder due to the significant formation of carbide layer on the top surface of the machined specimen which increase the micro-hardness thus leading to crack formation and propagation.
