Vol. 26 No. 1 2024 3 EDITORIAL COUNCIL EDITORIAL BOARD EDITOR-IN-CHIEF: Anatoliy A. Bataev, D.Sc. (Engineering), Professor, Rector, Novosibirsk State Technical University, Novosibirsk, Russian Federation DEPUTIES EDITOR-IN-CHIEF: Vladimir V. Ivancivsky, D.Sc. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Vadim Y. Skeeba, Ph.D. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Editor of the English translation: Elena A. Lozhkina, Ph.D. (Engineering), Department of Material Science in Mechanical Engineering, Novosibirsk State Technical University, Novosibirsk, Russian Federation The journal is issued since 1999 Publication frequency – 4 numbers a year Data on the journal are published in «Ulrich's Periodical Directory» Journal “Obrabotka Metallov” (“Metal Working and Material Science”) has been Indexed in Clarivate Analytics Services. Novosibirsk State Technical University, Prospekt K. Marksa, 20, Novosibirsk, 630073, Russia Tel.: +7 (383) 346-17-75 http://journals.nstu.ru/obrabotka_metallov E-mail: metal_working@mail.ru; metal_working@corp.nstu.ru Journal “Obrabotka Metallov – Metal Working and Material Science” is indexed in the world's largest abstracting bibliographic and scientometric databases Web of Science and Scopus. Journal “Obrabotka Metallov” (“Metal Working & Material Science”) has entered into an electronic licensing relationship with EBSCO Publishing, the world's leading aggregator of full text journals, magazines and eBooks. The full text of JOURNAL can be found in the EBSCOhost™ databases.
OBRABOTKAMETALLOV Vol. 26 No. 1 2024 4 EDITORIAL COUNCIL EDITORIAL COUNCIL CHAIRMAN: Nikolai V. Pustovoy, D.Sc. (Engineering), Professor, President, Novosibirsk State Technical University, Novosibirsk, Russian Federation MEMBERS: The Federative Republic of Brazil: Alberto Moreira Jorge Junior, Dr.-Ing., Full Professor; Federal University of São Carlos, São Carlos The Federal Republic of Germany: Moniko Greif, Dr.-Ing., Professor, Hochschule RheinMain University of Applied Sciences, Russelsheim Florian Nürnberger, Dr.-Ing., Chief Engineer and Head of the Department “Technology of Materials”, Leibniz Universität Hannover, Garbsen; Thomas Hassel, Dr.-Ing., Head of Underwater Technology Center Hanover, Leibniz Universität Hannover, Garbsen The Spain: Andrey L. Chuvilin, Ph.D. (Physics and Mathematics), Ikerbasque Research Professor, Head of Electron Microscopy Laboratory “CIC nanoGUNE”, San Sebastian The Republic of Belarus: Fyodor I. Panteleenko, D.Sc. (Engineering), Professor, First Vice-Rector, Corresponding Member of National Academy of Sciences of Belarus, Belarusian National Technical University, Minsk The Ukraine: Sergiy V. Kovalevskyy, D.Sc. (Engineering), Professor, Vice Rector for Research and Academic Aff airs, Donbass State Engineering Academy, Kramatorsk The Russian Federation: Vladimir G. Atapin, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Victor P. Balkov, Deputy general director, Research and Development Tooling Institute “VNIIINSTRUMENT”, Moscow; Vladimir A. Bataev, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Vladimir G. Burov, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Aleksandr N. Korotkov, D.Sc. (Engineering), Professor, Kuzbass State Technical University, Kemerovo; Dmitry V. Lobanov, D.Sc. (Engineering), Associate Professor, I.N. Ulianov Chuvash State University, Cheboksary; Aleksey V. Makarov, D.Sc. (Engineering), Corresponding Member of RAS, Head of division, Head of laboratory (Laboratory of Mechanical Properties) M.N. Miheev Institute of Metal Physics, Russian Academy of Sciences (Ural Branch), Yekaterinburg; Aleksandr G. Ovcharenko, D.Sc. (Engineering), Professor, Biysk Technological Institute, Biysk; Yuriy N. Saraev, D.Sc. (Engineering), Professor, V.P. Larionov Institute of the Physical-Technical Problems of the North of the Siberian Branch of the RAS, Yakutsk; Alexander S. Yanyushkin, D.Sc. (Engineering), Professor, I.N. Ulianov Chuvash State University, Cheboksary
Vol. 26 No. 1 2024 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Kuts V.V., Oleshitsky A.V., Grechukhin A.N., Grigorov I.Y. Investigation of changes in geometrical parameters of GMAW surfaced specimens under the infl uence of longitudinal magnetic fi eld on electric arc....................................... 6 Saprykina N.А., Chebodaeva V.V., Saprykin A.А., Sharkeev Y.P., Ibragimov E.А., Guseva T.S. Optimization of selective laser melting modes of powder composition of the AlSiMg system................................................................. 22 Gubin D.S., Kisel’ A.G. Features of calculating the cutting temperature during high-speed milling of aluminum alloys without the use of cutting fl uid............................................................................................................................................. 38 EQUIPMENT. INSTRUMENTS Borisov M.A., Lobanov D.V., Zvorygin A.S., Skeeba V.Y. Adaptation of the CNC system of the machine to the conditions of combined processing...................................................................................................................................... 55 Nosenko V.A., Bagaiskov Y.S., Mirocedi A.E., GorbunovA.S. Elastic hones for polishing tooth profi les of heat-treated spur wheels for special applications..................................................................................................................................... 66 Podgornyj Y.I., Skeeba V.Y., Martynova T.G., Lobanov D.V., Martyushev N.V., Papko S.S., Rozhnov E.E., Yulusov I.S. Synthesis of the heddle drive mechanism....................................................................................................... 80 MATERIAL SCIENCE Ragazin A.A., Aryshenskii V.Y., Konovalov S.V., Aryshenskii E.V., Bakhtegareev I.D. Study of the eff ect of hafnium and erbium content on the formation of microstructure in aluminium alloy 1590 cast into a copper chill mold............................................................................................................................................................................ 99 Zorin I.A., Aryshenskii E.V., Drits A.M., Konovalov S.V. Study of evolution of microstructure and mechanical properties in aluminum alloy 1570 with the addition of 0.5 % hafnium........................................................................... 113 Karlina Y.I., Kononenko R.V., Ivantsivsky V.V., Popov M.A., Deryugin F.F., Byankin V.E. Relationship between microstructure and impact toughness of weld metals in pipe high-strength low-alloy steels (research review)..................... 129 Patil N.G., Saraf A.R., Kulkarni A.P Semi empirical modeling of cutting temperature and surface roughness in turning of engineering materials with TiAlN coated carbide tool................................................................................. 155 Sawant D., Bulakh R., Jatti V., Chinchanikar S., Mishra A., Sefene E.M. Investigation on the electrical discharge machining of cryogenic treated beryllium copper (BeCu) alloys........................................................................................ 175 Karlina A.I., Kondratiev V.V., Sysoev I.A., Kolosov A.D., Konstantinova M.V., Guseva E.A. Study of the eff ect of a combined modifi er from silicon production waste on the properties of gray cast iron................................................. 194 EDITORIALMATERIALS 212 FOUNDERS MATERIALS 223 CONTENTS
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Investigation on the electrical discharge machining of cryogenic treated beryllium copper (BeCu) alloys Dhruv Sawant 1, a, Rujuta Bulakh 1, b, Vijaykumar Jatti 1, c, *, Satish Chinchanikar 2, d, Akshansh Mishra 3, e, Eyob Messele Sefene 4, 5, f 1 Symbiosis Institute of Technology, Pune-412115, Maharashtra State, India 2 Vishwakarma Institute of Information Technology, Kondhwa (Budruk), Pune - 411039, Maharashtra, India 3 School of Industrial and Information Engineering, Politecnico Di Milano, 22 Leoanardo str., Milan, Italy 4 National Taiwan University of Science and Technology, 43 Keelung Rd., Taipei, 106335, Taiwan 5 Bahir Dar Institute of Technology, Bahir Dar, Amhara, Ethiopia a https://orcid.org/0009-0009-9543-690X, dhruv.sawant.btech2022@sitpune.edu.in; b https://orcid.org/0009-0000-4594-3385, rujuta.bulakh.btech2022@sitpune.edu.in; c https://orcid.org/0000-0001-7949-2551, vijaykumar.jatti@sitpune.edu.in; d https://orcid.org/0000-0002-4175-3098, satish.chinchanikar@viit.ac.in; e https://orcid.org/0000-0003-4939-359X, akshansh.mishra@mail.polimi.it; f https://orcid.org/0000-0003-4660-6262, eyobsmart27@gmail.com Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2024 vol. 26 no. 1 pp. 175–193 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2024-26.1-175-193 ART I CLE I NFO Article history: Received: 18 November 2023 Revised: 08 January 2024 Accepted: 22 January 2024 Available online: 15 March 2024 Keywords: Beryllium copper Cryogenic treatment Material removal rate White layer thickness Surface crack formation ABSTRACT Introduction. In modern manufacturing world, industries should adapt technological advancements for precision machining of diffi cult-to-machine metals, especially for beryllium copper (BeCu) alloys. The electrical discharge machining of alloys has proven its viability. The purpose of the work. A literature review indicated that the investigation of electrical discharge machining of BeCu alloys is still in its infancy. Furthermore, the cryogenic treatment of workpieces and electrodes in electrical discharge machining has not received much attention from researchers. Moreover, the impact of magnetic fi eld strength on surface integrity and productivity during electrical discharge machining has not attracted much attention from researchers. The methods of investigation. This paper describes the use of electrolytic copper with diff erent gap current values, pulse on periods, and external magnetic strength for electrical discharge machining of BeCu alloys. This paper examines how the material removal rate, the thickness of the white layer, and the formation of surface cracks are aff ected by cryogenic treatment of the workpiece and tool, pulse-on time, gap current, and magnetic strength. Results and Discussion. The combination of the cryogenically treated BeCu workpiece and the untreated Cu electrode had the highest material removal rate among all the combinations of workpieces and tools used in this study. The pulse on-time and the strength of the magnetic fi eld had little infl uence on material removal rate, whereas the gap current had the greatest eff ect. The maximum achieved material removal rate was 11.807 mm3/min. At a high material removal rate, the observed thickness of the white layer on the horizontal surface ranged from 12.92 μm to 14.24 μm. In the same way, the maximum and minimum values for the vertical surface were determined to be 15.58 μm and 11.67 μm, respectively. According to scanning electron microscopy, the layer thickness was less than 20 μm, and barely noticeable surface cracks were observed in specimens with low, medium and high material removal rates. Obviously, due to the cryogenic processing of the workpiece and the external magnetic strength, there was a slight cracking of the surface and the formation of a white layer. For citation: Sawant D., Bulakh R., Jatti V., Chinchanikar S., Mishra A., Sefene E.M. Investigation on the electrical discharge machining of cryogenic treated beryllium copper (BeCu) alloys. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2024, vol. 26, no. 1, pp. 175–193. DOI: 10.17212/1994-6309-2024-26.1-175-193. (In Russian). ______ * Corresponding author Jatti Vijaykumar S., Ph.D. (Engineering), Professor Symbiosis Institute of Technology, Pune – 412115, Maharashtra State, India Tel.: 91-2028116300, e-mail: vijaykumar.jatti@sitpune.edu.in
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Introduction BeCu alloys, or beryllium copper alloys, are very reliable materials with outstanding fatigue strength, hardness, wear resistance, and non-magnetic characteristics that are utilized in a variety of industries. A consistent, homogeneous liquid solution is obtained by combining beryllium and copper, which is a distinctive feature of the microstructure. Copper frequently retains its face-centered cubic form, and beryllium becomes a crucial part of the copper crystal. When copper atoms are replaced by beryllium atoms in the same lattice regions, a substitutional solid solution is produced. BeCu alloys have been used to create breaker reeds, diaphragms, control valves, switchgear components, and all varieties of fl at and coil springs. High electrical conductivity and toughness have also been used in plastic extrusion dies and specialty tooling. However, there are several problems when utilizing traditional machining methods to cut BeCu alloys. Due to the high strength of BeCu alloys, it is problematic to maintain the integrity of the surface of the fi nished product, and increased tool wear occurs during machining. BeCu alloys have good thermal and electrical properties, which make electrical discharge machining safe and eff ective. For cutting hard materials, electrical discharge machining (EDM) is a practical technique [1–6]. Due to the complexity of the process, numerous studies on electrical discharge machining have been conducted to determine its’ optimal parameters [7–10]. The main objective of this research is to develop a production system that improves material removal rate (MRR). Using machine learning (ML) techniques, a group of researchers created performance prediction models for EDM, including MRR [11–13]. EDM process modeling development was discussed in detail by Ming et al. [14]. Shastri et al. [15] assessed the eff ects of cooling, ultrasonic machining, powder mixture machining, and cryogenic machining on performance indicators such MRR, tool wear rate (TWR), surface integrity, and recast layer. Boopathi [16] off ered a comprehensive analysis of the literature on diff erent dielectric fl uids, previously unknown and sustainable innovations, process parameters, machining characteristics, and optimization strategies used in various dry and near-dry EDMs. The purpose of combining dry and near-dry EDM research was to support environmentally friendly EDM research projects. The impact of EDM die sinking settings on the MRR of BeCu alloys was examined by Ali et al. [17]. The eff ects of EDM settings on the MRR, tool wear, relative electrode wear, and surface roughness of NiTi alloys were examined by Daneshmand et al. [18]. The voltage, discharge current, pulse-on time, and pulse-off time are some of these parameters. The tests were designed using the L18 orthogonal matrix using the Taguchi methodology. The eff ects of current, voltage, tool rotation, Al2O3 powder, MRR, TWR, and surface roughness were examined by Daneshmand et al. [19]. The results show that the MRR can be increased by using Al2O3 powder, rotating the tool, and raising the voltage, current strength, and pulse width. The eff ects of electrical discharge machining on the environment, human health, and safety were examined by Baroi et al. [20]. The eff ects of cryogenic treatment on Inconel 718 work material were investigated by Kannan et al. [21]. The cooling eff ect of copper electrodes during the electrical discharge die sinking of a titanium alloy (Ti-6Al-4V) was investigated by Abdulkareem et al. [22]. The eff ects of cooling on workpiece surface roughness and electrode wear have been studied. In order to fi nd out how the Ti 6246 alloy’s machinability was infl uenced by deep cryogenic treatment, Gill and Singh [23] used an electrolytic copper tool to drill blind holes 10 mm in diameter. Furthermore, a comparison was conducted between the untreated Ti 6246 alloy and the deep cryogenically treated Ti 6246 alloy in terms of surface roughness and overcut of holes. Copper electrode cooling during electrical discharge machining (EDM) of a workpiece composed of M2-grade high-speed steel was investigated by Srivastava and Pandey [24]. Machinability was evaluated using electrode wear ratio (EWR) and surface roughness (SR). A study by Yildiz et al. [25] investigated the eff ect of cryogenic and cold processing on the EDM machinability of BeCu alloy workpieces. The BeCu alloy was treated at temperatures of about −150°F (−100 °С) for cold treatment and −300°F (−185 °С) for cryogenic treatment in this investigation. The titanium EDM machining properties were studied by Singh and Singh [26] both before and after the tool and workpiece were cryogenically treated. The study’s output metrics included dimensional accuracy, surface roughness, TWR, and MRR. Copper’s thermal conductivity was greatly enhanced by
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 cryogenic treatment in an experimental study conducted by Nadig et al. [27]. The thermal conductivity was only marginally enhanced by tempering as compared to cryogenic treatment. The results pave the way for further research to optimize temperature and duration of cryogenic treatment as well as other tempering parameters. During the EDM of high-speed steel M2, Srivastava and Pandey [28] assessed surface roughness (SR), material removal rate (MRR), and electrode wear ratio (EWR) using an ultrasonicassisted cryogenically cooled copper electrode. The discharge current, duty cycle, gap voltage, and pulseon time were the variables that could be adjusted during the process. In the electrical discharge machining process, three types of electrodes were compared: conventional, cryogenically cooled, and cryogenically cooled together with ultrasound. The MRR, EWR, and SR were measured. The reattachment of particles to the machined surface caused major diffi culties in dry EDM, according to Liqing and Yingjie [29]. Their research proposed two methods for increasing MRR in dry EDM: the fi rst involves the use of cryogenically cooled workpieces, and the second involves the use of dry EDM in combination with oxygen gas. Electrical resistivity, crystallite size, microhardness, and microscopic studies were provided by Jaff erson and Hariharan [30], and a comparison of the machining performance of cryogenically treated and untreated microelectrodes in MEDM was carried out. The eff ect of cryogenically treated tool electrodes on electrical discharge machining (EDM) processes was studied by Mathai et al. [31]. When machining is performed using electrodes subjected to cryogenic treatment of varying durations, the effi ciency of the process is examined by examining the change in critical response characteristics, such as MRR, TWR, and surface roughness, with respect to current and pulse-on time. The study conducted by Singh et al. [32] aimed to evaluate the eff ectiveness of the copper electrode manufactured through a novel fast manufacturing process in EDM on D-2 steel. On the other hand, Prakash et al. [33] focused on comparing the performance of untreated and cryogenically treated micro-EDM tool electrodes while machining the magnesium alloy AZ31B. The tool electrodes were subjected to cryogenic treatment to enhance its mechanical characteristics, such as hardness and wear resistance, which in turn improved the quality of the machined features. A group of researchers optimized the process parameters using multi-criteria decision-making (MCDM) during the EDM of AA6061-T6 SiC composites (15 wt. % SiC) [34]. Attempts were made using supervised machine learning to predict the EDM surface roughness of deep cryogenically treated NiTi, NiCu and BeCu alloys [35]. [35]. A review of the literature showed that the research on electrical discharge machining of BeCu alloys is still in its infancy. Furthermore, the cryogenic treatment of workpieces and electrodes in EDM has not received much attention from researchers. Moreover, the impact of magnetic fi eld strength on surface integrity and productivity during EDM has received very little attention in research. Therefore, the goal of this study is to ascertain how the material removal rate, thickness of the white layer, and creation of surface cracks are aff ected by a cryogenically treated workpiece and electrode, magnetic strength, gap current, and pulse on time. In addition, this study makes use of machine learning regression algorithms to estimate the MRR. The remainder of the work consists of sections devoted to materials and methods, results and their discussion, as well as conclusions. Materials and Design In this study, an Electronica Machine Tools Limited die sink-type electrical discharge machine, model C400x250, was used for testing. A block of 100×100×50 mm in size was used as a workpiece in this study, which was then divided into blocks of 30×20×20 mm in size for carrying out experiments. Copper with high thermal conductivity was used as the tool electrode material in the experiments. The tool had a square shape with dimensions of 6×90 mm, respectively. Using an indexing system and a milling machine, it was given a 3×25 mm square shape. During the experiment, an external magnetic fi eld was applied using a neodymium magnet surrounding the cutting zone. The workpiece and tool electrodes were cryogenically prepared prior to the experiment. Electrical resistance/conductivity tests were conducted to determine how cryogenic treatment aff ected the materials. The weight of the workpieces and tool electrodes was measured using a computerized weighing
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 scale with a minimum count of 0.001 g both before and after machining. The material removal rate was calculated using Eq. 1. 1 2 ñ W W MRR T æ - ÷ö = ç ÷ ç ÷ çè ´ ø , (1) where W1 is the mass of the workpiece before machining, (g); W2 is the mass of the workpiece after machining, (g); ρ is the density of the workpiece, (gm/cm3); T is the cycle time, (min). Fig. 1. Experimental set-up Ta b l e 1 Design variables Parameters Performance measures Gap current (A): 8, 10, 12,14 16 Material removal rate, white layer thickness, and crack length Magnetic strength (T): 0, 0.124, 0.248, 0.372, 0.496 Pulse on time: 38 μs Gap voltage: 55 V Pulse off time: 7 μs Dielectric: Commercial EDM oil Flushing pressure: 0.5 Kg/cm2 Polarity: Workpiece (-ve); Tool electrode (+ve) The thickness of the white layer of each specimen was examined at 850× magnifi cation using a scanning electron microscope. Next, the treated surfaces of the specimens were examined at 1000× magnifi cation and surface cracks on the bottom and walls of the holes were measured. Using electrolytic copper tool electrodes, square holes with a depth of 5 mm from the surface were created on untreated BeCu alloy parts. Figure 1 shows the experimental setup, which consisted of a BeCu workpiece, copper tool electrode, and magnets used for experimentation. A BeCu workpiece drilled with square holes with copper tool electrodes and magnets in the cutting zone. Experiments were carried out to understand the eff ect of cryogenic treatment of the workpiece and tool electrodes, along with the gap current and external magnetic strength, on the material removal rate. Thus, the experiments were carried out in two stages: a pilot study and main experiments based on the Box–Behnken design. To study the eff ects of the process parameters on the performance characteristics, the design variables are listed in Table 1.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 To make a decision on the range and level of gap current and magnetic fi eld to obtain optimal values of material removal rate, pilot studies were carried out. The gap current and the gap current were varied at fi ve levels; one pass was performed at each level. Various combinations of workpiece and tool were considered: – BeCu (untreated) and Cu (untreated); – BeCu (untreated) and Cu (cryogenically treated); – BeCu (cryogenically treated) and Cu (untreated); – BeCu (cryogenically treated) and Cu (cryogenically treated). Based on the results obtained from the pilot study, the main experiments were designed using a threevariable Box–Behnken design. Results and Discussion This section illustrates the MRR experimental results and its analysis, white layer thickness and crack formation and prediction of MRR using machine learning regressions. Experimental results and analysis Experimental study was carried out in two phases. Firstly, one variable was varied over the selected levels at the fi xed average values of the other variables. These experiments were conducted to study and normalize the EDM machine settings and process responses in general. It was determined that 5 mm was the proper depth of milling to achieve stability while the process was underway. Two variables were modifi ed in this study: gap current and magnetic strength. The remaining variable was spread at equal intervals throughout its range, while the other variables were fi xed at its respective average values for the whole range of options available in the machine. In the fi rst fi ve experiments, only the gap current was changed, as is illustrated in Table 2. A similar variation was observed in the magnetic strength in fi ve experiments as shown in Table 3. The gap current and magnetic strength varied for four workpiece and tool combinations. Ta b l e 2 Experimental matrix: Varying gap current Magnetic strength (T) Gap voltage (V) Gap current (A) Pulse on time (μs) Pulse off time (μs) Workpiece and tool combinations (U:U, T:U, U:T, and T:T) 0.248 55 8 38 7 U:U (BeCu-untreated with Cu-untreated), T:U (BeCu-treated with Cu-untreated), U:T (BeCu-untreated with Cu-treated), T:T (BeCu-treated with Cu-untreated) 0.248 55 10 38 7 0.248 55 12 38 7 0.248 55 14 38 7 0.248 55 16 38 7 Ta b l e 3 Experimental matrix: Varying magnetic strength Magnetic strength (T) Gap voltage (V) Gap current (A) Pulse on time (μs) Pulse off time (μs) Workpiece and tool combinations (U:U, T:U, U:T, and T:T) 0 55 12 38 7 U:U (BeCu-untreated with Cu-untreated), T:U (BeCu-treated with Cu-untreated), U:T (BeCu-untreated with Cu-treated), T:T (BeCu-treated with Cu-untreated) 0.124 55 12 38 7 0.248 55 12 38 7 0.372 55 12 38 7 0.496 55 12 38 7
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 In this study, only the gap current and external magnetic fi eld was varied. It is known that the most infl uential parameter for the maximum MRR is the spark energy. During cryogenic treatment, the thermal vibration of atoms in metals decreases due to the temperature decrease. This results in a decrease in electrical resistivity and improved electrical conductivity. Owing to the cryogenic process, the homogeneity of the crystal structure increases, and the gaps and dislocations are dissolved, which improves the structural compactness and electrical conductivity. According to the Wiedmann-Franz-Lorenz law, an increase in electrical conductivity would increase thermal conductivity. Figure 2 depicts MRR varying with gap current for treated and untreated BeCu alloys with treated and untreated copper tool electrodes (four workpiece and tool combinations – U:U, T:U, U:T, and T:T). The surface temperature of the workpiece tends to increase as a result of the increase in spark energy caused by the gap current. The substance melts as a result, and the molten metal is subsequently fl ushed away by the dielectric fl uid. Due to the increased electrical conductivity of the workpiece after cryogenic treatment, the MRR increases. Debris from the undesired material removed from the workpiece is created in the machining zone during the EDM process. The machining effi ciency is decreased because arcing occurs instead of sparking if it is not removed from the cutting zone. Debris removal from the cutting zone is facilitated by the strength of the external magnetic fi eld. Additionally, this keeps the particles in the cutting zone from clogging As a result, the stability of the EDM process is improved. Figure 3 depicts MRR varying with magnetic fi eld strength for treated and untreated BeCu alloys with treated and untreated copper tool electrodes (four workpiece and tool combinations – U:U, T:U, U:T, and T:T). With an increase in the gap current, the spark energy increases, increasing the surface temperature of the workpiece, thereby melting and evaporating material from the workpiece surface and increasing MRR. Fig. 2. MRR varying with gap current for four workpiece and tool combinations Fig. 3. MRR varying with magnetic strength for four workpiece and tool combinations To understand the eff ect of input variables, namely the gap current (Ig), external magnetic fi eld strength (B), and pulse-on time (Ton), on the material removal rate (MRR) was investigated for cryogenically treated BeCu workpiece and untreated Cu electrode combination. This combination of workpiece and the tool is selected as it provided higher MRR among the other combinations of workpiece and the tool selected in the present study. Table 4 depicts the experimental matrix with MRR varying with Ig, B, and Ton. Experimentally based mathematical model (Eq. 2) was developed for the MRR for the T:U (BeCu-treated with Cu-untreated), workpiece and tool combination, for better understanding the EDM performance. The values of the coeffi cients involved in the equation were calculated using the Microsoft Advanced Excel data analysis tool. R-squared (R2) values which measure variation proportion in the data points are close to 0.912. Therefore, the developed model is reliable to predict the MRR during EDM of cryogenically treated BeCu workpiece with untreated Cu electrode. 1.339 0.00121 1.0508 0.004501( ) ( ) ( ) on MRR Ig B T = . (2)
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Ta b l e 4 Box–Behnken Design with observed values of MRR Exp. No. Gap current (Ig) (A) Magnetic fi eld (B) (T) Pulse on time (Ton) (μs) MRR (mm3/min) 1 8 NO 26 2.32 2 8 0.496 26 2.22 3 16 NO 26 6.00 4 16 0.496 26 6.54 5 12 NO 13 1.93 6 12 0.496 13 2.04 7 12 NO 38 4.66 8 12 0.496 38 5.003 9 8 0.248 13 0.97 10 16 0.248 13 1.88 11 8 0.248 38 2.89 12 16 0.248 38 7.40 13 12 0.248 26 4.86 14 12 0.248 26 4.64 15 12 0.248 26 4.78 Further, to have a better understanding of the eff ect of process parameters, MRR (fi gure 4) is plotted using the developed model varying with process parameters for the T:U (BeCu-treated with Cu-untreated), workpiece and tool combination. Figure 4, a depicts MRR varying with gap current at magnetic strength and pulse on time of 0.248 T and 26 s. The MRR can be seen as increasing with the gap current. a b c Fig. 4. MRR varying with Gap current (a), Magnetic fi eld (b), and Pulse on time (c) The MRR that changes with magnetic fi eld at a gap current of 12 A and a pulse on time of 26 s is shown in fi gure 4, b. Furthermore, MRR fl uctuates with pulse on time at gap current and magnetic strength of 12 A and 0.248 T, as shown in fi gure 4 c. A slight increase in MMR is observed with increasing magnetic strength. However, as demonstrated in fi gure 4 , the MRR seems to increase with the pulse on time. The gap current has the biggest impact on the MRR, followed by the timing of the pulse and the magnetic fi eld strength, which has a negligible eff ect. According to fi gure 4, MRR values decrease with decreasing magnetic fi eld and gap current values. As the values of gap current and magnetic fi eld increase, the MRR also increases. With a magnetic fi eld of 0.4 T and a gap current of 16 A, the MMR exceeds 7 mm3/min. Lower magnetic fi eld and pulse on time values result in lower MRR readings. MRR increases simultaneously with an increase in magnetic fi eld and pulse on time values. MRR exceeds 7 mm3/min with a magnetic fi eld of 0.4 T and a pulse on time of 35 μs.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 MRR values are lower for lower gap current and pulse on time values. As the gap current and pulse on time increase, the MMR also increases. With a current in the interelectrode gap of 16 A and a pulse interval of 35 μs, the SMR exceeds 7 mm3/min. With a gap current of 16 A, a magnetic induction of 0.4709 T and a pulse of 38 μs, the optimizer, using the principle of complex desirability, timely predicted the MRR value of 7.6453 mm3/min. White layer thickness (WLT) As for the primary tests, the conditions that provided the highest rate of material removal were selected to test the white layer thickness (WLT). The thickness of the white layer is shown on the two separate edges of the square holes in fi gure 5, a and b for gap current of 8 A, magnetic strength of 0.248 T, gap voltage of 55 V, pulse on time of 13 μs and pulse off time of 7 μs. Figure 5 shows that the low spark energy at 8 A gap current and 13 μs pulse on duration resulted in limited white layer formation. It should be noted that the workpiece has a very low carbon content, which means that a white layer of less thickness is formed. Figure 6, a and b illustrate the thickness of the white layer at two distinct corners of the square hole when the gap voltage is 55 V, the gap current is 8 A, the magnetic strength is 0.248 T, the pulse-on time is 38 μs, and the pulse-off time is 7 μs. Because of the higher spark energy in this trial circumstance compared to the prior case, there is a greater thickness of the white layer. The white layer thickness at two separate square hole edges is depicted in fi gure 7, a and b with gap currents of 16 A, magnetic strengths of 0.248 T, gap voltages of 55 V, pulse on time of 38 μs, and pulse off times of 7 μs. In this scenario, the processing conditions are higher: the pulse on time is 38 μs and the gap Fig. 5. WLT for Expt. 9 (Table 4) at the vertical cross-section of a square hole (a), at the horizontal cross-section of the square hole (b) Fig. 6. WLT for Expt. 14 (Table 4) at the vertical cross-section of a square hole (a), the horizontal cross-section of the square hole (b)
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Fig. 7. WLT for Expt. 12 (Table 4) at the vertical cross-section of a square hole (a), the horizontal cross-section of the square hole (b) current is 16 A. Thus, the white layer in this case is thicker than in the fi rst two. However, the thickness of the white layer is typically less than 20 μm, indicating that molten metal is eff ectively removed from the workpiece surface by dielectric fl ushing. The white layer refers to a thin layer of recast material that forms on the surface of the workpiece after the electrical discharge process. This layer has diff erent physical and chemical properties compared to the base material. The thickness of the white layer depends on various factors, including the EDM process parameters and the material being machined. Higher discharge energy increases material removal, resulting in a thicker white layer. Longer pulses provide greater energy transfer and may result in the formation of a thicker white layer. BeCu alloy has specifi c thermal and electrical conductivity properties that can aff ect the white layer formation. The composition and microstructure of the alloy can also play a role. Proper fl ushing of the machining zone helps remove debris and control the heat generated during the process, which can infl uence the white layer formation. The observed white layer thickness at a lowmaterial removal rate for the horizontal surface is a minimum of 6.38 μm and a maximum of 10.47 μm. Similarly, for the vertical surfaces, the maximum and minimum are found to be 13.83 μm and 6.99 μm, respectively. The observed white layer thickness at a high material removal rate on the horizontal surface is at least 12.92 μm and a maximum of 14.24 μm. Similarly, for the vertical surface, the maximum and minimum are found to be 15.58 μm and 11.67 μm, respectively. Crack formed on the machined surface The EDM process involves the generation of high temperatures on the workpiece surface. Rapid heating and subsequent cooling cycles can induce thermal stresses. These thermal stresses can lead to crack formation. Adequate cooling and fl ushing of the machining zone are crucial in EDM to control the temperature and remove debris. Insuffi cient fl ow or cooling of the dielectric fl uid can result in excessive heating and thermal stress, increasing the likelihood of crack formation. Figure 8, a and b and fi gure 9? a–d show the crack and recast layer on the machined surface of the workpiece. The cut section of the workpiece was examined using scanning electron microscopy. Photographs were taken of the bottom surface of the workpiece and the wall surface (fi gure 9 e, f). The specimen has very few surface cracks at low, medium and high material removal rates because the workpiece has superior thermal properties and a thinner white layer is formed on the surface. Cryogenic treatment of the workpiece and external magnetic strength prevented the formation of surface cracks and the formation of white layers. Conclusions In the current study, the material removal rate, white layer thickness, and crack formation on the walls and bottom surface of a square hole produced by electrical discharge machining (EDM) were investigated by considering the eff ects of cryogenically machined combinations of copper-beryllium (BeCu) workpieces
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Fig. 8. Cracks for Expt. 9 at the wall surface of square hole (a); at the bottom surface of square hole (b) Fig. 9. Cracks at the wall surface of square hole for Expt. 14 (a); at the bottom surface of square hole for Expt. 14 (b); at the wall surface of square hole for Expt. 12 (c); at the bottom surface of square hole for Expt. 12 (d)
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 and copper (Cu) electrodes. Experiments were carried out with varying the gap current, magnetic fi eld strength, and pulse on time. The pulse turn off time of 7 μs and the gap voltage of 55 V were kept constant for all experiments. The thickness of the white layer and the formation of surface cracks were also investigated as a function of the EDM process parameters. To determine the fi nal process input parameter levels for the primary experiments, an pilot study was fi rst conducted. Second, the Box-Behnken design of experiments was followed in the planning and execution of the primary studies. Based on the experiments, a mathematical model was created to predict and maximize MRR by optimizing EDM performance. This study allows us to draw the following conclusions. ● The cryogenically treated BeCu workpiece and untreated Cu electrode combination provided higher MRR among the other combinations of workpiece and the tool selected in the present study. ● The gap current had the biggest impact on the MRR, followed by the timely pulse and the magnetic fi eld strength, which had a negligible eff ect. The MRR was a minimum of 0.9 mm3/min and a maximum of 11.807 mm3/min. ● The observed white layer thickness at a low material removal rate for the horizontal surface was a minimum of 6.38 μm and a maximum of 10.47 μm. Similarly, for the vertical surfaces, the maximum and minimum were 13.83 μm and 6.99 μm, respectively. ● The observed white layer thickness at a high material removal rate on the horizontal surface was a minimum of 12.92 μm and a maximum of 14.24 μm. Similarly, for the vertical surface, the maximum and minimum were 15.58 μm and 11.67 μm, respectively. ● SEM images were obtained on the wall and bottom surfaces of the workpiece. Negligible surface cracks were observed for low, medium, and high material removal rates. ● It is evident that, owing to the cryogenic treatment of the workpiece and external magnetic strength, the white layer formation and surface crack formation were low. References 1. Vora J., Khanna S., Chaudhari R., Patel V.K., Paneliya S., Pimenov D.Y., Giasin K., Prakash C. Machining parameter optimization and experimental investigations of nano-graphene mixed electrical discharge machining of nitinol shape memory alloy. Journal of Materials Research and Technology, 2022, vol. 19, pp. 653–668. DOI: 10.1016/j.jmrt.2022.05.076. 2. Akıncıoğlu S. Taguchi optimization of multiple performance characteristics in the electrical discharge machining of the TiGr2. Facta Universitatis. Series: Mechanical Engineering, 2022, vol. 20 (2), pp. 237–253. DOI: 10.22190/FUME201230028A. 3. Danish M., Al-Amin M., Abdul-Rani A.M., Rubaiee S., Ahmed A., Zohura F.T., Ahmed R., Yildirim M.B. Optimization of hydroxyapatite powder mixed electric discharge machining process to improve modifi ed surface features of 316L stainless steel. Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering, 2023, vol. 237 (3), pp. 881–895. DOI: 10.1177/09544089221111584. 4. Kam M., İpekçi A., Argun K. Experimental investigation and optimization of machining parameters of deep cryogenically treated and tempered steels in electrical discharge machining process. Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering, 2022, vol. 236 (5), pp. 1927–1935. DOI: 10.1177/09544089221078133. 5. Gautam N., Goyal A., Sharma S.S., Oza A.D., Kumar R. Study of various optimization techniques for electric discharge machining and electrochemical machining processes. Materials Today: Proceedings, 2022, vol. 57, pp. 615–621. DOI: 10.1016/j.matpr.2022.02.005. 6. Shukla S.K., Priyadarshini A. Application of machine learning techniques for multi objective optimization of response variables in wire cut electro discharge machining operation. Materials Science Forum, 2019, vol. 969, pp. 800–806. DOI: 10.4028/www.scientifi c.net/MSF.969.800. 7. Kumar Vin., Kumar Vik., Jangra K.K. An experimental analysis and optimization of machining rate and surface characteristics in WEDM of Monel-400 using RSM and desirability approach. Journal of Industrial Engineering International, 2015, vol. 11 (3), pp. 297–307. DOI: 10.1007/s40092-015-0103-0. 8. Kumar S.V., Kumar M.P. Optimization of cryogenic cooled EDM process parameters using grey relational analysis. Journal of Mechanical Science and Technology, 2014, vol. 28, pp. 3777–3784. DOI: 10.1007/s12206014-0840-9.
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