Optimization of Electrical Discharge Coating Process Using MOORA Based Firefly Algorithm

Electrical discharge machining (EDM), a thermo-mechanical machining process, is used in producing a complicated intrinsic cavity in difficult-to-machine materials with excellent surface finish. One of the major disadvantages of EDM process is the tool wear. However, tool wear can be used advantageously for coating purpose. Coating is a unique method of EDM process by the use of electrode prepared through powder metallurgy (PM) route. This process is also cheaper as compared to other deposition processes like chemical vapor deposition (CVD) and physical vapor deposition (PVD) processes. Therefore, electrical discharge coating (EDC) can be employed in industries for coating purpose where the corrosion resistance and hardness of the work piece material are required to be increased for their use in a wide range of environmental condition. Copper (Cu) and tungsten (W) powders in weight percentage of 30 and 70 respectively are used for the preparation of the tool electrode. The PM process parameters like compaction pressure (CP) and sintering temperature (ST) are varied to prepare the tool electrodes. The density and electrical conductivity of the electrodes are found to increase with an increase in compaction pressure and sintering temperature. The substrate on which coating is made is chosen as AISI 1040 stainless steel with EDM oil as the dielectric fluid. During coating, the influence of parameters like discharge current (Ip), duty cycle (τ) and pulse-on-time (Ton) on material deposition ratio (MDR), Average surface roughness (Ra), coated layer thickness (LT) and micro-hardness of the coated layer are studied. To reduce the number of the experiment, Taguchi’s L₁₈ orthogonal array has been used. To find out the best parametric combination that can simultaneously optimize all performance measures, multi-objective optimization on the basis of ratio analysis (MOORA) method combined with Firefly algorithm has been employed.