The present study highlights a multi-objective optimization problem by applying utility concept coupled with Taguchi method through a case study in CNC end milling of UNS C34000 medium leaded brass. The study aimed at evaluating the best process environment which could simultaneously satisfy multiple requirements of surface quality. In view of the fact, the traditional Taguchi method cannot solve a multi-objective optimization problem; to overcome this limitation, utility theory has been coupled with Taguchi method. Depending on Taguchi’s Lower-the-Better (LB) response criteria; individual surface quality characteristics has been transformed into corresponding utility values. Individual utility values have been aggregated finally to compute overall utility degree which serves as representative objective function for optimizing using Taguchi method. Utility theory has been adopted to convert a multi-response optimization problem into a single response optimization problem; in which overall utility degree serves as the representative single objective function for optimization. The study of combined utility theory and Taguchi method for predicting optimal setting. Based on Taguchi’s Signal-to-Noise ratio (S/N), analysis has been made on the overall utility degree and optimal process environment has been selected finally which corresponds to highest S/N Ratio. Optimal result has been verified through confirmatory test. The case study indicates application feasibility of the aforesaid methodology proposed for multiresponse optimization and off-line control of multiple surface quality characteristics in CNC end milling.

In order to machine hard and high-strength-to-weight ratio materials, electrical discharge machining (EDM) process is extensively used in aerospace, automobile and other industrial applications. However, high erosion of tool and improper selection of machining variables have emerged as a major obstruction to achieveproductivity in this direction. High erosion of tool not only enhances the cost of machining but also increases the machining time by causing interruption during machining. Therefore, proper selection of machining variables and tool material life are the two vital aspects for the tool engineers working in EDM. In view of this, the present work proposes an extensive experimental investigation and optimization of machining variables of cryogenically treated brass tool materials on machining competences of Inconel 718 workpiece. The study primarily highlightsthe outcome of cryogenically treated soaking duration of tools along with other important process variables, viz. discharge current, open-circuit voltage, pulse-on time, duty factor and flushing pressure, on the performance measures such as electrode wear ratio (EWR), surface roughness and radial over-cut. The study revealed that soaking duration in deep cryo-treatment of the electrode is a significant variable to achieve improved machining characteristics. The performance measures are converted into equivalent single performance measure by calculating the relative closeness coefficient by the techniques for order preferences by similarity to ideal solution (TOPSIS) approach. Finally, a novel teaching–learning-based optimization (TLBO) algorithm has been proposedto find the optimal level of machining variables for the performance measures. The optimal levels of cutting variables obtained through the algorithm are validated through confirmation test, predicting an error of 2.171 percentages between the computational and experimental results. The predicted result suggests that theproposed model can be used to select the ideal process states to achieve productivity for the cryo-treated EDM.

Laser drilling is a popular method as it eliminates the problem of chatter and vibration due to the absence of physical contact between the tool and workpiece. Tool breakage, a common phenomenon that occurs due to bending of the tool in making of slender holes using conventional drilling, can also be avoided. However,quality of the hole measured in terms of circularity, taper and spatter area is the major concern during laser drilling. The present investigation attempts to find out the optimum parametric setting during drilling of Ti6Al4V using CO₂ laser in order to achieve quality holes. Experiments have been conducted to assess the influence of machining parameters, viz. flushing pressure, laser power and pulse frequency, on the performance characteristics such as taper of kerf, heat-affected zone (HAZ) and spatter area. Taguchi’s L₉ orthogonal array has been used to design the experimental layout as it reduces the experimental cost and time. Analysis of variance has been performed to assess the effect of machining parameter on the performance characteristics. It has been observed that laser power has significant influence on taper of kerf, HAZ and spatter area. Based ondesirability approach, the study suggests that all the performance characteristics can be simultaneously optimized at flushing pressure of 40 Pa, laser power of 2250 W and pulse frequency of 1600 Hz. The study also presents a numerical model to simulate the laser drilling process. Since comparison of experimental andnumerical model shows a relative error within 10%, adequacy of the numerical model for assessment of quality characteristics of laser drilled holes is justified.