# Principles and Characteristics of Different EDM Processes in Machining Tool and Die Steels
###### Abstract
Several review papers related to EDM were published in recent years such as references [29, 30, 31, 32, 33, 34, 35], among others. Furthermore, some other articles presented a discussion of specific objectives; for example, [PERSON] et al. [36] developed a model for prediction of material removal rate (MRR) and tool wear rate (TWR) for the EDM of AISI D6 tool steel. They reported that higher values of pulse-on time resulted in higher MRR and lesser TWR. [PERSON] et al. [37] used powder-mixed EDM for machining die steels. Titanium powder was used for mixing, and surface quality was analyzed. It was revealed that the quality of surface layer was improved at optimal parameters. [PERSON] et al. [38] studied the effects of the key input variables of wire EDM of ASP30 tool steel. The output responses under consideration were MRR and surface roughness. The results revealed that an increase in spraying pressure of dielectric fluid led to a higher MRR and surface roughness. EDM of AISI M42 high-speed tool steel alloy was conducted to study the effect of major input parameters on MRR. It was revealed that tool polarity was the most influential factor and, at negative polarity, maximum MRR was achieved. P20 tool steel was machined using wire EDM, and pulse-on time, pulse-off time, peak current, and spark gap voltage were varied. The output responses under study were kerf width and MRR. The best combination of parameters was reported to achieve maximum MRR [39]. [PERSON] and [PERSON] [40] applied rotary-EDM to machine AISI D2 tool steel using a copper electrode. MRR, TWR, and machining rate were studied by varying input parameters (peak current, voltage, duty cycle, and electrode rotation speed). [PERSON] et al. [41] conducted experiments to study the effect of major input variables on MRR, electrode wear ratio, and surface roughness while machining H13 die steel. It was reported that higher MRR and lower electrode wear rate were achieved using a copper electrode, whereas lower surface roughness was attained with a brass electrode. [PERSON] et al. [42] compared the performance of unprocessed and equal channel angular pressing (ECAP)-processed copper electrode while machining AISI H13 tool steel using EDM. It was reported that the triple-ECAP-passed electrode gave better machining quality. Despite many existing review papers, to the best of authors' knowledge, there is no study that reviewed the EDM process specifically for tool and die steels. Since tool and die steels have usage in a wide range of applications and they are difficult to cut with the conventional manufacturing processes, non-conventional processes such as EDM are becoming prevalent for their machining. Generally, one of the largest uses of the EDM process is in tool-, die-, and mold-making. All these industries mostly use various kinds of tool steels. EDM remains one of the most popular processes used for their fabrication. Therefore, it is important to have in-depth knowledge of this subject and, hence, the aim of this research paper is to provide comprehensive information and details of this process. It is important for review articles such as this one to bring out the intricacies of processes, parameter-response co-relations, and critical analysis of their response to better utilize them. This will prove to be of great use to understand failures, as well as in-service performance issues, of tools and tooling. The present article aims to provide an overview of the significant contributions of EDM to machining of tool steels. This paper gives the state of the art on current research studies conducted in all EDM variants for machining different grades of tool materials. The paper begins with a brief introduction of EDM and its variants, and then introduces its working principle. It further discusses the EDM process parameters and its performance measures. The main text of this article provides a meticulous review on major areas of EDM research using different grades of tool materials.