New Electrode Profile for Machining of Internal Cylindrical Surfaces by Electrochemical Drilling

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1 New Electrode Profile for Machining of Internal Cylindrical Surfaces by Electrochemical Drilling Hamdy K. 1, Mohamed M. K. 1, 2 and Abouelmagd G. 1 1 El-Minia University, Faculty of Engineering, Production Eng.& Machine Design Dept., Egypt 2 Taif University, Faculty of Engineering, Mechanical Engineering., Saudi Arabia Abstract: Electrochemical machining (ECM) is one of non-traditional machining process. It offers the ability to machine extremely hard materials or materials that are difficult to be machined using conventional methods. Moreover, it is considered one of the most effective ways to machine the complex shapes of internal and external geometries. This paper introduces a new electrode tool drilling with insert tip instead of traditional die electrode tool shape used in machining of internal cylindrical shapes. It reviews the development of high efficiency and low cost electrode for electrochemical cylindrical machining. The effect of insert tool profile on current values, metal removal rate (MRR), conicity, and surface roughness is investigated. Based on the experiments, it is concluded that by using the proposed insert tip tool profile, the hole machining becomes more accurate with smoother surface roughness with a remarkable reduction in the value of the consumed current. Index New Tip electrode, electrochemical machining, drilling. I. INTRODUCTION In last Decades, the mechanical properties of engineering materials especially in the hardness have been developed. All traditional methods of machining, like hole drilling or polishing are usually carried out according to the typical pattern that a tool of very hard material (i.e. diamond) is used for scraping out the softer material of the workpiece (typically metal alloys or steel substrates), [1, 2]. Therefore, the tool of machining processes suffers from short life and high cost which are added to the cost of product. So nontraditional machining appears to solve those problems. Electrochemical machining (ECM) is one of the nonconventional machining processes, [3]. Electrochemical machining (ECM) is a modern machining process that relies on the removal of workpiece molecules by electrochemical dissolution in accordance with the principle of faraday [4]. It solves the problem of the tool life and neglects the cost of tool which affects the product cost. ECM is ideally suited to the machining of the complex shaped components made from high strength heat resistance 1 alloys. A current is made to pass between a cathode (tool) and anode (workpiece) through an electrolyte. The gap between the tool and workpiece is typical below 1.0 mm and this together with a D.C. voltage of value ranging between 6.0 to 24.0 volts produce very high current density by Faraday's law of electrolysis. The only reaction to take place at the tool surface is the gap evolution and thus the tool isn't subjected to erosion and retains its shape throughout the process. The power transmitted across the electrode gap is sufficient to cause a static electrolyte to evaporate. To keep the electrolyte at the required temperature it is pumped through the gap at velocities of up to 30.0 m/s and allowed to cool in setting tanks. This high flow velocity also flushes the reaction products from the gap reducing harmful build-ups and ensuring reasonable consistent electrolyte conductivity throughout the gap. ECM can be carried out in either of two basic modes. Firstly the tool remains stationary during the process and as machining proceeds the gap widens. Secondly the tool is fed towards the work such that the feed rate exactly matches the erosion rate on the work surface. In this mode dynamic equilibrium is stained in which the gap size remains constant [5]. ECM however does not produce thermal or mechanical stresses and can machine high performance metals without heat-damaged layer and produce no tool wear [6]. ECM is an electrochemical dissolution process that can remove electrically conductive materials regardless of their hardness and toughness. It produces smooth and burr free surfaces [7,8]. ECM process were originally designed for manufacturing components in military and aerospace industries and have been extended to many other fields such as the automotive industries, die manufacturing, electrical equipment, and more recently, microsurgical components [3]. The element of electrochemical sinking (ECS), the tool and workpiece are connected to the negative and positive terminals of a DC power supply respectively [5]. An electrolyte is pumped from electrolyte tank, with high velocity to flow between the tool (cathode) and the workpiece (anode) [3,5,9-12]. The tool (the cathode) is moved in the direction of metal removal and the machining gap is maintained at specified minimal value, the shape of

2 Theo. Exp. Voltage Tool Feed Rate Rotational Electrode Linear Electrode Current Metal Removal Rate Conicity and Accuracy Surface Roughness References INTERNATIONAL JOURNAL OF CONTROL, AUTOMATION AND SYSTEMS VOL.2 NO.3 October 2013 the tool will be accurately duplicated in workpiece (the anode) the cavity in the workpiece will have the shape and size corresponding to those of the tool. Electrochemical drilling with stationary electrodes produces an inaccurate and irregular hole profile. For the electrochemical drilling, it is concluded that a slow relative rotary motion between the electrodes helps to produce the machined profile of better quality [13]. Hocheng et al. [15] predicted the profile of hole in the boring process. They discussed evolve and propagation of hole and the profile of it with flat end ended electrode. Mahdavinejad et al. [16] designed rifling tool for barrel rifling in the inner surface of complex shape. They tool theoretical and experimental and they found that quite matched between them. Wang et al. [17] proposed an electrochemical drilling method with vacuum extraction of electrolyte, flow distributing along the machining gab with different electrolyte flow pattern are compared numerically and experimentally. Hocheng et al. [18] utilized a computer model to predict the erosion profile during ECM in use a simple flat ended electrode, it s observed that the produced diameter of workpiece of a hole can be controlled mostly with machining time, while other conditions apply mild effect. Rajurkar et al. [19] present the latest advances and the principles issued in ECM development. Zhu et al. [20] present a method of improving machining accuracy in ECM by using a dual pole tool with metallic bush outside the insulated coating of a cathode tool. Although close attention was paid to cathode tool design on the introduction of ECM into manufacturing industries, tool design remains a major challenge [8]. The design of a suitable tool for a desired workpiece shape, and dimension forms a major problem. The workpiece shape is expected to be greater than the tool size by an oversize [4]. Cathode design mainly deals with the determination of tool shape which will produce a workpiece with prescribed dimension and accuracy. Ideally, it should be implemented by performing a simple calculation at the outset of the design procedure, but this not yet practical due to the complex gap configuration interactively affected by many process variables. Tool shape is seldom a perfect negative image of that of the workpiece. Prediction of the tool shape is a formidable inverse boundary problem of Laplace's equation. This problem requires adjustment of a free boundary (tool) to satisfy imposed boundary conditions at both electrodes. Difficulties in designing ECM tools stem from a lack of adequate understanding of ECM dissolution phenomena and mathematical complexities. Present methods of tool design only allow calculation of a first approximation to the final shape. The subsequent adjustment of tool shape is still done empirically in practice. The iterative procedure of tool design is a time consuming process, resulting in costly machine down and long lead-times [8]. The material used for ECM tools should be electrically conductive and easily machine able to the required geometry. The various materials used for this purpose 2 include copper, brass, stainless steel, titanium, and copper tungsten [4]. Table 1 shows the summary of electrochemical hole drilling as previous work with different machining parameters. No. Table1: Summary of previous work with different machining parameters Theoretical or Experimental Machining Conditions Machining Quality [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] Ibrahim A., M. [2] Kamel, M.A. [5] Zhaoyang et al. [6] Zhu et al. [7] Osman, H.M. [10] Thanigaivel an et al. [11] Hocheng et al. [15] Mahdavinej ad et al. [16] Wang et al. [17] Hocheng et al. [18] Bhattachary ya et al [19] Zhu et al. [20] The present work provides an experimental investigation of the effect the proposed electrode profile on the accuracy of machined profile and power consumption. II. EXPERIMENTAL WORK The equipment of electrochemical machining includes DC power supply, pump, electrolytic tank and tool. The representative experimental set-up is schematically illustrated in figure 1. This group was intended to study the effect of new electrode profile at constant electrolyte velocity, voltage (V) and tool feed rate (f), on electrolyzing current(i), metal removal rate (MRR), hole conicity (k), and surface roughness (R a ). Table 2 shows the machining parameters used in the process. Figure 2 shows the tool profile dimensions using in experimental work.

3 make a cylindrical hole cutting and the new electrode with insert tip to reduce the power consumed machining by reducing the cutting current. Table 3: Different types of drilling tools in ECM. Tradiotional ECM Drilling Fig.1: Schematic Diagram of the experimental setup. Table2: Machining Conditions: Machining conditions 1 Voltage Applied Voltage 22 volt Type Na Cl solution 2 Electrolyte Concentration 200 gm./liter Flow rate 18 liter/min Temperature 18 o 25 o Material Brass 3 Tool/Cathode (-) speed Feed Rate 0.8 mm/min Rotational 15.4 rpm 4 Workpiece/Anode (+) Material Steel Initial gap 0.5mm 5 Gap thickness Tool with linear feed Suggestion ECM Drilling Tool with linear and rotational feed New electrode porfile (the proposed electrode profile) III. RESULTS AND DISCUSSION Figure 3 shows the effect of traditional electrode die profile and the proposed tip electrode at the same cutting condition. It is found that at 0.4 mm tip thickness, the current consumption reduced by 31% approximately, at 0.6 mm tip thickness the current consumption reduced by 50 % approximately and at 0.7 mm tip thickness the cutting current consumption reduced by 40 % approximately. It can be concluded that the new electrode consumes low current Figures 4 and 5 show the effect of the tip dimensions on the current. It is observed that the current differs between 40 and 55 amperes. This behavior can be explained on the basis that the area of cutting fits the area of tip so that the current passes through tight gap and it suppresses the current and just allows it to cut the workpiece. Figure 2: Sketch of the tool profile used in experimental. Table 3 shows firstly the tool profile using in all previous work or common ECD with negative die tool with linear feed rate and with linear feed rat plus rotational electrode to 3

4 Figure 3: Comparison between current consumed by different electrode (tool) types. Figure 6: Effect of height of tip on current density. Figure 4: Effect of height of tip on current. Figure 5: Effect of the thickness of tip on current. Figures 6 and 7 show the effect of the tip dimensions on the current density at 0.8 mm/min feed rate. In figure 12, it is observed that the current density decreases with increasing height of tip. That behavior can be explained on the fact that as the area of cutting increases height increases, while the current does not exceed 5 amperes..figure 7: Effect of thickness of tip on current The effect of the tip dimensions on the metal removal rate (MRR) is discussed in this section. Figure 8 shows the effect of dimensions of tip height on the metal removal rate at feed of 0.8 mm/min for drilling hole. The experimental results indicate that the metal removal rate increases with increasing of the height of the tip. That may be explained as follows: the pilot of tool, as shown in figure 4, starts machining and opens the initial hole, moreover, it smoothens the way for machining of tip then the tip starts machining and completes the operation until the end. The tip almost is cut so it overcomes the disadvantage of bare type of tool which has lateral cutting. The machining depends on the tip and the height of it so that more height causes more machining and causes more metal removal rate. 4

5 Figure 8: Effect of height of tip on metal removal rate (MRR) Figure 9 shows the effect of tip thickness on the metal removal rate at feed of 0.8 mm/min for drilling hole. It clears that the metal removal rate increases with increasing the thickness of tip because of the current density increases with increasing the thickness of tip but the current in thickness 0.6 mm drops and affects the current density which causes drop in metal removal rate and there is small error in devices which observes the results, where the drop can be ignored because of the drop does not exceed 0.25 gm. /min Figure 10: Effect of height of tip on conicity.. Figure 11 shows the effect of the tip thickness on the conicity at 0.8 mm/min feed rate. It clears that the conicity decreases as the thickness of tip increases. This behavior can be explained as the high thickness gives more area of cutting that gives more accurate dimensions and low hole distortion. Figure 9: Effect of thickness of tip on metal removal rate (MRR). Figure 10 shows the effect of dimension of tip height on the conicity at 0.8 mm/min feed for drilling hole. It is observed that the conicity increases as the height of tip increases but the conicity drops as the height equals 15 mm. At 5 and 10 mm height of tip the conicity is high because of the lateral machining and the cutting action of body tool. As a result of that the uniform distributed machining on the circumference of hole is missed and inaccurate. At 15 mm tip height the tip cuts with small lateral cutting. Figure 11: Effect of thickness of tip on conicity. Figures 12 and 13 show the effect of the tip dimensions on the conicity at feed rate 0.8 mm/min. It clears that the surface roughness is less than 1 µm Ra and that behavior can be explained as the machining by that electrode profile is by the tip hence the area of cutting tip is so small with small side effect of tool of very high polishing surface. 5

6 IV. Figure 12: Effect of height of tip on surface roughness. Figure 13: Effect of thickness of tip on surface roughness. CONCLUSION It is found that the new profile presents high accuracy of conicity compared to the normal tool. It is reported that the surface roughness is very smooth so that no finishing machining is required. The new profile decreases the cost equipment by using small power supply that generates low current. REFERENCES [1]. Thomas W.: High rate electrochemical dissolution of iron based alloys in NaCl and NaNO3 electrolytes. Ph.D. Thesis, School of Chemistry, University of Stuttgart, [2]. Ibrahim, A, M.: Investigation of Some Electrochemical Machining Parameters for Internal Conical Shapes. M.Sc. Thesis, Faculty of Engineering, Minia University, [3]. McGeough, J.A.: Principles of Electrochemical Machining. Chapman and Hall Ltd, [4]. El Hofy, H.A.: Advanced Machining Processes. McGraw-Hill,New York, [5]. Kamel, M.A.: An Investigation into Electrochemical Sinking. M.Sc. Thesis, Faculty of Engineering, Minia University, [6]. Zhaoyang Zhang, Di Zhu, Ningsong Qu, Minghuan Wang: Theoretical and experimental investigation on electrochemical Micromachining. In: Microsyst Technol, Vol.13, PP ,2007 [7]. D. Zhu, K. Wang, J. M. Yang : Design of Electrode Profile in Electrochemical Manufacturing Process. Research Center for Nontraditional Machining, College of Mechanical and Electrical Engineering, Nanjlng University of Aeronautics and Astronautics, China,2003 [8]. K.P. Rajurkar l, D.Zhu', J.A. McGeough, J. Kozak, A. De Silva: New Developments in Electro-Chemical Machining. In: Annals of the ClRP Vol. 48 No.2,1999. [9]. Wilson, J.F.: Practice and theory of electrochemical machining. In: JohnWiley& Sons Inc., New York, [10]. Osman, H.M. Investigation of some electrochemical machining parameters. M.Sc. Thesis, Faculty of Engineering, Minia University, May 1983 [11]. R. Thanigaivelan, R. M. Arunachalam, Pelden Drukpa: Drilling of micro-holes on copper using electrochemical micromachining. In: Int J Manuf Technol, Vol.61, PP ,2012 [12]. Zhaoyang Zhang, Di. Zhu, Ningsong Qu., Minghuan Wang: Theoretical and experimental investigation on electrochemical Micromachining. In: Microsyst Technol., Vol. 13, PP ,2007 [13]. H.Hocheng, P.S.Pa.: A review of electrode design for electrochemical drilling and electro polishing of holes. In: electrochemistry, Vol.12, PP ,2007 [14]. Mallick, U., "Estimation of MRR using U-shape electrode in electrochemical machining" M.Sc. Thesis, Institute of technology Rourkela,2009 [15]. H. Hocheng, P.S. Kao, S.C. Lin.: Development of the eroded opening during electrochemical boring of hole. In: Manuf Technol, vol.25,pp ,2005 [16]. R. A. Mahdavinejad, M. R. Hatami: ECM rifling tool design and manufacturing.. In: Iranian Journal of Science & Technology, Transaction B, Engineering, Vol. 32PP , The Islamic Republic of Iran, [17]. W. Wang, D. Zhu, N.S. Qu, S.F. Huang, X.L. Fang: Electrochemical drilling with vacuum extraction of electrolyte. In: Journal of Materials Processing Technology, Vol.210, PP ,2010 [18]. H. Hocheng, Y.H. Sun, S.C. Lin, P.S. Kao: A material removal analysis of electrochemical machining using flat-end cathode. In: Journal of Materials Processing Technology Vol. 140, PP ,2003 [19]. S. Bhattacharyya, A. Ghosh, A.K. Mallik: Cathode shape prediction in electrochemical machining using simulated cut-and-try procedure. In: Journal of Materials Processing Technology Vol. 66, pp ,1997 [20]. D. Zhu, H.Y.Xu.: Improvement of electrochemical machining accuracy by using dual pole tool. In: Journal of materials processing technology, Vol. 129, PP ,2002 Eng. K. Hamdy Authors: Bibliography eng_khaled2222@mu.edu.eg Hamdy K, was born in Kuwait, in 1986 with Egptian nationality.he received the B.Sc. degree in production and machine design dept. from El- Minina university, Egypt, He worked for El-fateh company for steel structures and sandwitch panels in its technical office since 2008 until Since 2010 he is working as a demonstrator in the department of prodution and machine design, Minia university, Egypt. He concerns with non conventional machining field specially ECM. 6

7 Associate Professor Dr. Ing. Mostafa Mohamed Mohammed M. K. Was born in Kena, Egypt, in He received the B.Sc. and M.SC. degrees in Production Engineering and Design dept. from El- Minia university Egypt, 92 and 96 respectively. He received the Ph.D degree in Mechanical Engineering Hannover university Germany, since 2010He is working as an Associate Professor in the Department of, Production Engineering and Design dept. El-Minia,. He is currently an Associate Professor in the Department of Mechanical Engineering, Faculty of Engineering, Taif University, Saudi Arabia, his publications about forty research in the fields of non-conventional machining (ECM,WJ and AWJ) and Tribology. Prof. Dr. Eng. Gamal El-Din Ali Abouelmagd Dean of the Faculty of Engineering, Minia University, Minia, Egypt G. Abouelmagd graduated from Faculty of Eng., Minia University, He held an M.SC degree from Minia University (1987) and Ph.D. Degree from Mechanical Engineering, Minia University- Technical Aachen University (Germany-Egypt Channel System), (1992). Working as a Professor from 29/08/2006 up to 2/07/2008 in Yanbu Industrial College, Yanbu, KSA. Professor, from 2008 tell now, in Production Engineering and Design Department, Minia University, Minia, Egypt. Dean of the Faculty of Engineering, Minia University, Minia, Egypt from 24/09/2008. Research Interests; Materials Characterization, for more information please visit web page: 7