Statistical modeling and optimization of process parameters in electro-discharge machining of cobalt-bonded tungsten carbide composite (WC/6%Co)

(BQ) In this paper, attempts have been made to model and optimize process parameters in Electro-Discharge Machining (EDM) oftungsten carbide-cobalt composite (Iso grade: K10) using cylindrical copper tool electrodes in planing machining mode based on statistical techniques.
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Statistical modeling and optimization of process parameters in electro-discharge machining of cobalt-bonded tungsten carbide composite (WC/6%Co)Available online at www.sciencedirect.comProcedia CIRP 6 (2013) 463 – 468toi ưu hoa dong thoi 3outputThe Seventeenth CIRP Conference on Electro Physical and Chemical Machining (ISEM)Statistical modeling and optimization of process parameters inelectro-discharge machining of cobalt-bonded tungsten carbidecomposite (WC/6%Co)S. Assarzadeh*, M. GhoreishiDepartment of Mechanical Engineering, K. N. Toosi University of Technology, P. O. Box: 19395-1999, Tehran, Iran.* Corresponding author. E-mail address: saeed_assarzadeh@yahoo.comAbstractIn this paper, attempts have been made to model and optimize process parameters in Electro-Discharge Machining (EDM) oftungsten carbide-cobalt composite (Iso grade: K10) using cylindrical copper tool electrodes in planing machining mode based onstatistical techniques. Four independent input parameters, viz., discharge current (A: Amp), pulse-on time (B: µs), duty cycle (C:%), and gap voltage (D: Volt) were selected to assess the EDM process performance in terms of material removal rate (MRR:mm3/min), tool wear rate (TWR: mm3/min), and average surface roughness (Ra: µm). Response surface methodology (RSM),employing a rotatable central composite design scheme, has been used to plan and analyze the experiments. For each processresponse, a suitable second order regression equation was obtained applying analysis of variance (ANOVA) and student t-testprocedure to check modeling goodness of fit and select proper forms of influentially significant process variables (main, two-wayinteraction, and pure quadratic terms) within 90% of confidence interval (p-value ≤ 0.1). It has been mainly revealed that all theresponses are affected by the rate and extent of discharge energy but in a controversial manner. The MRR increases by selectingboth higher discharge current and duty cycle which means providing greater amounts of discharge energy inside gap region. TheTWR can be diminished applying longer pulse on-times with lower current intensities while smoother work surfaces are attainablewith small pulse durations while allotting relatively higher levels to discharge currents to assure more effective discharges as wellas better plasma flushing efficiency. Having established the process response models, a multi-objective optimization techniquebased on the use of desirability function (DF) concept has been applied to the response regression equations to simultaneously finda set of optimal input parameters yielding the highest accessible MRR along with the lowest possible TWR and Ra within theprocess inputs domain. The obtained predicted optimal results were also verified experimentally and the values of confirmationerrors were computed, all found to be satisfactory, being less than 10%. The outcomes of present research prove the feasibility andeffectiveness of adopted approach as it can provide a useful platform to model and multi-criteria optimize MRR, Ra, and TWRduring EDMing WC/6%Co material.© 2013 The Authors. Published by Elsevier B.V. Open access under CC BY-NC-ND license.© 2013 The Authors. Published by Elsevier B.V. Professor Bert LauwersSelection and/or peer-review under responsibility of Selection and/or peer-review under responsibility of Professor Bert LauwersKeywords: Electro-Discharge Machining (EDM); Design of Experiments (DOE); Response Surface Methodology (RSM); Desirability FunctionApproach (DFA); Process Modeling; Multi-Objective Optimization.1. IntroductionElectro-Discharge Machining (EDM), the oldest andmost popular non-traditional machining method, is anelectro-thermal process where a work piece electrode,usually submerged in a liquid dielectric medium, isshaped through the action of a succession of highfrequency discrete electrical discharges (sparks)produced by a DC pulse generator. Every spark locallyerodes (melts and vaporizes) tiny amount of the materialsurface, the overall effect being a cavity as thecomplementary shape of tool electrode geometry overthe work. The applicability of EDM process is oftenrationalized when other machining methods, especiallyconventional ones, lack efficiency and productivity inresponse to materials which have complex and difficultto-machine structural properties. Amongst suchmaterials, tungsten carbide cobalt composites (WC-Co)are regarded as the most important engineering materialswith extreme applications in today’s global competitivemarkets where high resistance over wear and abrasion isneeded; especially in production lines, manufacturingcarbide dies, cutting tools, forestry tools and so on.Nowadays, the EDM process has been recognized as thebest and perhaps the only feasibly economical way ofmachining WC-Co composites [1]. However, unlikesteel, available in miscellaneous types and grades, o ...