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Cryogenic Treatment (CT) is basically the process of deep-freezing materials at cryogenic temperatures in order to enrich mechanical and physical properties of materials. The execution of cryogenic processing on tool materials is expected to improve wear resistance, hardness, and dimensional stability; reduce tool consumption and down time for the setup, thus incurring substantial cost reduction. Additionally, CT of work material prior to EDM may be proved beneficial in terms of remarkable improvement in the material properties as it may relieve residual stresses, promote grain refinement, and improve electrical as well as thermal properties. Therefore, application potential of cryogenically treated tool/workpiece in the context of electro-discharge machining specially on ‘difficult-to-cut’ materials has been reported in literature.

Gill and Singh (2010) investigated the effect of Deep Cryogenic Treatment (DCT) on

machinability of Ti 6246 alloy in electric discharge drilling with electrolytic Copper tool. The authors attempted to compare the production accuracy of holes drilled in deep cryogenically treated Ti 6246 (DCT Ti 6246) alloy and non-treated Ti 6246 alloy in terms of surface roughness and overcut. Improved material removal rate and wear ratio, lower tool wear rate were observed in case of EDD of DCT Ti 6246 alloy workpiece as compared with non-treated work material. Also, superior production accuracy of holes

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was reported while EDD of DCT workpiece. Srivastava and Pandey (2012a, b) performed parametric study on EDM process using ultrasonic assisted cryogenically cooled Copper electrode during electro-discharge machining of M2 grade high speed steel. In this work, electrode wear ratio, material removal rate, and surface roughness were analyzed. Discharge current, pulse-on time, duty cycle and gap voltage were considered as the controllable process variables. The MRR, Electro Wear Rate (EWR) and SR obtained in EDM process with normal electrode, cryogenically cooled electrode and ultrasonic assisted cryogenically cooled electrode were compared. Thus, in the present work the aforesaid process route was recommended superior in performances than conventional EDM process due to better tool life, satisfactory tool shape retention ability and better surface integrity.

Kapoor et al. (2012) investigated the effect of deep cryogenic treatment on the brass wire

electrode used in wire electrical discharge machining on EN31 work material. In this work, the microstructure and crystalline phase of deep and non-treated brass wire electrodes was observed. More refined structure was observed in case of deep cryogenic treatment. Improved electrical conductivity was obtained for the deep cryogenically treated tool electrode. The effect of deep cryogenic treatment on the brass wire electrode was also investigated for the performance of wire electrical discharge machining. Taguchi experimental design was applied to investigate the optimal parameters for maximum material removal rate. The ANOVA analysis indicated that type of wire, pulse width, time between two pulses and wire tension were the significant factors to achieve maximum material removal rate. Jafferson and Hariharan (2013) reported a comparative study on machining performance of both cryogenically treated and untreated micro electrodes in micro-EDM along with electrical resistivity, crystallite size, micro-hardness and microscopic analysis. From the study, significant reduction of 58% in tool wear rate was observed for Tungsten electrode followed by brass and Cu electrodes with 51% and 35%, respectively.

Khanna and Singh (2016) presented a comparison for normal and cryogenically treated

high Carbon high Chromium cold alloy tool (D-3) steel for execution of WEDM process. The response variables namely cutting rate, metal removal rate, and surface roughness were considered, and six input process parameters like pulse width, time between two pulses, servo reference mean voltage, short pulse time, maximum feed rate, and wire mechanical tension were used for evaluating overall machining performance. Sharma et

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off time, servo voltage, and peak current) on surface roughness of the WEDMed D-2 tool steel specimens. In order to increase the wear resistance, the cryogenically treated workpiece was used herein. The Mathematical modeling of the process was carried with the help of response surface methodology. It was observed that pulse-on time imposed the maximum effect on surface roughness.

Srivastava and Pandey (2014) studied the effect of discharge current, pulse-on time, duty

cycle, and gap voltage on electrode wear ratio, material removal rate, and surface roughness for EDM of M2 grade High Speed Steel (HSS) workpiece using cryogenically cooled electrode. The analysis revealed that discharge current, pulse-on time, and duty cycle significantly affected EWR and MRR. Discharge current and pulse-on time were found to be the most influential factors in affecting SR. Dhobe et al. (2014) studied the effect of WEDM parameters on surface finish of cryogenically treated AISI D2 tool steel.

Kumar et al. (2015) attempted an experimental investigation towards machining of three

grades of Titanium alloy TITAN 15, TITAN 21, and TITAN 31 using powder mixed electro-discharge machining in order to study the effect of cryogenic treatment of tool/work material and its effect on tool wear rate.

Kumar et al. (2016a) investigated the effect of cryogenic treatment on the machining

performance of Ti–5Al–2.5Sn alpha Titanium alloy during electric discharge machining. Untreated, shallow cryogenically treated (-1100C), and deep cryogenically treated (- 1840C) Titanium alloys were machined by varying current and pulse-on time. The machining performance was evaluated in terms of higher material removal rate, higher micro-hardness, lesser tool wear rate, and lesser surface roughness. The results showed significant improvement in the machining performance with deep cryogenically treated alloy when compared with shallow and untreated alloy. Hui et al. (2016) investigated discharge characteristics and discharge gap whilst machining of Ti–6Al–4V alloy by cryogenically cooled tool electrode during electro-discharge machining in distilled water using the monopulse discharge method. The influence of the cryogenically cooled tool electrode on the discharge gap and the initial maintaining voltage between the electrode and workpiece were analyzed under various temperatures. A comparative experiment of machining Ti–6Al–4V alloy was carried out by using cryogenically cooled tool electrode EDM and conventional EDM. Lower electrode wear, higher material removal rate, and higher corner size machining accuracy were obtained by using cryogenically cooled tool electrode EDM.

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Gaikwad and Jatti (2016) focused on optimization of electro-discharge machining process

parameters for maximization of material removal rate while machining of cryogenically treated NiTi alloy. In this study, gap current, pulse-on time, pulse-off time, workpiece electrical conductivity, and tool conductivity were considered as process variables. It was found that work electrical conductivity, gap current and pulse-on time were the significant parameters that affected the material removal rate. Kumar et al. (2016b) investigated on improvement in EDMed work surface properties of cryogenically treated Titanium alloy after Powder-Mixed Electro-Discharge Machining (PMEDM) process. In this work, peak current was observed as the highly influential parameter that affected the micro-hardness as well as surface quality of the machined surface.