Form tolerance analysis and multi-parametric optimization of meso deep square hole EDMed on Inconel-718 plate using GRA method Sandeep Kumar Mechanical Engineering, Anna University Chennai, Chennai, India, and S. Dhanabalan Mechanical Engineering, M. Kumarasamy College of Engineering, Karur, India Abstract Purpose – The main objective of this experimental work is to analyze and measure the form tolerances namely flatness and squareness while machining a meso deep hole in EDM on Inconel-718 material plate. Design/methodology/approach – The experiments were performed on 15 amps rated SPARKONIX-EDM as per DOE (design of experiments). Kerosene was used as a dielectric along with constant pressure of 0.2 kg/cm 2 for all trial runs. The currents T on and T off were selected as process constraints to conduct experimental trials. The MRR, EWR, machining time and form tolerances were considered as output responses. The experimental outcomes were optimized by hybrid optimization using Taguchi and GRA (grey relational analysis) method. Findings – The EDM process parameters for Ni-based super alloy namely Inconel-718 had optimized by using GRA method coupled with Taguchi method. The optimum solution has been calculated for MRR, EWR, machining time and form tolerances namely squareness and flatness. The optimized parameters for the output responses in EDM process are Peak current (Ip) 12 Amps, 400 ms T on (pulse on time) and 10 ms T off (pulse off time). An attempt had also been made to attain Max. and Min. Evaluation of MRR and form tolerances, respectively. The attained optimum outcomes had also been examined through a real experiment and established to be satisfactory. Practical implications – This article will facilitate the defense, aerospace and EDM industries to improve their productivity with closer tolerances. Originality/value – The optimized parameters by multi-parametric optimization showed the considerable improvement in the process and will facilitate the defense, aerospace and EDM industries to improve their productivity with closer tolerances. Keywords Electrical discharge machining (EDM), Square-shape brass electrode, Material removal rate (MRR), Coordinate measurement machine (CMM), Grey relational analysis (GRA), Multi-parametric optimization Paper type Research paper 1. Introduction Electrical discharge machining (EDM) is a spark erosion machining process in which the removal of material takes place due to erosion caused by electric sparks. This process is utilized for machining of any conductive material irrespective of hardness. Highly precise products with square and flat surfaces are manufactured by non-conventional machining methods in various industries. Therefore, it is the requirement that regular estimations Form tolerance analysis This manuscript represents valid work and the author has no conflict of interests. Authors acknowledge that no funding has been granted/received for this research study and for preparation of this manuscript. The current issue and full text archive of this journal is available on Emerald Insight at: https://www.emerald.com/insight/2043-9377.htm Received 17 July 2019 Revised 24 November 2019 22 May 2020 28 July 2020 Accepted 11 September 2020 Grey Systems: Theory and Application © Emerald Publishing Limited 2043-9377 DOI 10.1108/GS-07-2019-0022