INFLUENCE OF MACHINE FEED RATE IN WEDM OF TITANIUM Ti-6Al-4V WITH CONSTANT CURRENT (6A) USING BRASS WIRE

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1 Available online at Procedia Engineering 41 (2012 ) International Symposium on Robotics and Intelligent Sensors 2012 (IRIS 2012) INFLUENCE OF MACHINE FEED RATE IN WEDM OF TITANIUM Ti-6Al-4V WITH CONSTANT CURRENT (6A) USING BRASS WIRE Aniza Alias a, Bulan Abdullah a *, Norliana Mohd Abbas a a Faculty of Mechanical Engineering, Universiti Teknologi MARA, Shah Alam, 40450, Selangor, Malaysia Abstract Wire electrical discharge machining (WEDM) technology is extensively used in the field of medical, mould making, aerospace and automobile industries. Improper electrical parameters settings can affect the processing efficiency and surface roughness due to arcing phenomenon that lead by discharge point of focus. Objective of the paper is to uncover the influence of three different machine rates which are 2 mm/min, 4 mm/min and 6 mm/min with constant current (6A) with WEDM of Titanium Ti-6Al-4V. The effects of different process parameters on the kerf width, material removal rate, surface roughness and surface topography are also discussed. The best combination of machining parameter viz. machine feed rate (4 mm/min), wire speed (8 m/min), wire tension (1.4kg) and voltage (60V) were identified. The paper highlights the importance of process parameters and different machining conditions on kerf width, MRR, surface roughness (Ra) and surface topography The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Centre of Humanoid Robots and Bio-Sensor (HuRoBs), Faculty of Mechanical Engineering, Universiti Teknologi MARA. Open access under CC BY-NC-ND license. Keywords: Wire Electrical Discharge Machining (WEDM), Titanium Ti-6Al-4V, Kerf Width, Material Removal Rate, Surface Roughness. 1. Introduction Wire electrical discharge machining (WEDM) is broadly used in machining of materials when precision is of major factor. WEDM is an ideal means for manufacturing such tooling because its ability to cut any conductive material regardless of hardness. The productivity of fabricating micro tools can be increased with the use of WEDM technology where more intricate tool geometries can be created with high quality. Material is eroded by series of discrete sparks between the work piece and a tool electrode (small wire) immersed in a liquid dielectric medium (deionized water). These electrical discharges melt and vaporize diminutive amounts of the work material, which are then ejected and flushed away by the dielectric. Since, the work piece and the electrode do not have mechanical contact, conductive material regardless of their hardness and toughness can be machined by WEDM [1]. It consume a continuously travelling wire electrode made of thin brass, copper or coated wire of diameter mm [2] which is capable to achieve very small corner radii and competency to machine precise, complex and irregular shape with high degree of accuracy and fine surface finish. As a result of the large number process variables and complex stochastic process mechanisms, selection of optimum machining parameter combinations for obtaining higher accuracy is a challenging task in WEDM. Some researchers, [1,3,4] investigated on the various aspects of the developments of electric discharge machining research which is optimizing the process variables, improving the performance measures, simplifying the electrode design and manufacture, monitoring and control of sparking process and surface quality improvement of WEDM process and so on. Qu et al. [5, 6] developed the cylindrical WEDM process and investigation of surface integrity and mechanical property of EDM surface layer. Onward, effects of the key parameters namely wire feed rate, pulse on-time and part rotational speed on the surface roughness and * Corresponding author: Tel.: ; fax: address: aliasaniza@gmail.com, bulanabdullah@gmail.com, lianabbas@gmail.com Published by Elsevier Ltd. doi: /j.proeng Open access under CC BY-NC-ND license.

2 Aniza Alias et al. / Procedia Engineering 41 ( 2012 ) roundness explored. They also proved that better material removal rate (MRR) could be achieved in cylindrical WEDM than in 2D wire EDM. In the aerospace and automotive industries, Titanium Ti-6Al-4V has great interest because of their high strength to weight ratios [7]. Into the bargain, the vulnerability of titanium to work harden during machining impairs their machinability hence they are referred to as difficult-to-machine materials [8] due to these alloys are not ductile and have low fracture toughness at room temperature [9]. The paper focused on the importance of kerf width, MRR, surface roughness (Ra) and surface topography and their strong dependence on the input parameters carried out on Titanium Ti-6Al-4V. Experiments were conducted by varying the machine feed rate with constant current, the corresponding values of the surface roughness and material removal rate are measured. 2. Materials and Method 2.1. Workpiece material Titanium Ti-6Al-4V has enormous importance in the aerospace industries. It reduces aircraft weight since the excellent strength-to-weight ratio and causes a reduction in fuel consumption and emissions. Titanium is replacing aluminium in many applications [10]. Besides the optimal features of titanium alloys, the usage is limited by the high costs, which arise because of the complex procurement process of titanium and processing difficulties such as poor machinability [11]. Titanium alloys are among the hardest materials to cut because of poor thermal conductivity, strength at high temperatures and chemical reactivity with tool materials [12]. This study applied Titanium Ti-6Al-4V work piece since only a few researchers have done the studies regarding this material using WEDM Wire Electrode Brass wire is widely used in WEDM processes due to its good machining properties and can be die-casted or extruded for specialized application. Some researchers [13, 14] used brass wire as the electrode of WEDM owing to its high tensile strength, high electrical conductivity, and good wire drawability to close tolerances. The ideal wire electrode material for this process has three important criteria i.e high electrical conductivity, sufficient mechanical strength and optimum sparks and flushes characteristics Dielectric Work pieces that are totally submerged in a tank filled with dielectric fluid grants temperature stabilization and efficient flushing especially when the work piece has varying thickness in WEDM process [1]. WEDM used deionised water instead of hydrocarbon oil as the dielectric fluid due to its low viscosity and rapid cooling rate [15] WEDM Parameter Setting A challenging task in WEDM is selection of optimum machining parameter combinations for obtaining higher accuracy large number due to process variables and complicated process mechanisms. The experiment were performed at three different machine feed rate with constant current, wire speed, wire tension and voltage as shown in Table 1. The selection of factors was based on the journals, preliminary result and the suggestion from the handbook recommended by the machine manufacturer. Table 1. WEDM Parameter Setting Parameter Experiment I Experiment II Experiment III Machine Feed Rate (mm/min) Current (A) Wire Speed (m/min) Wire Tension (kg) Voltage (Volts)

1808 Aniza Alias et al. / Procedia Engineering 41 ( 2012 ) 1806 1811 2.5.

3 1808 Aniza Alias et al. / Procedia Engineering 41 ( 2012 ) Sample Preparation and Experimental Procedure All specimens were cleaned in an alcohol bath using Mini Ultrasonic Cleaner model MUC-100 and then dried using Beuhler Metaserv Specimen Dryer in blower mode. After that, the specimens were kept in Buehler Specimen Cabinet Storage to prevent the formation of oxide on the surface. Titanium Ti-6Al-4V workpieces are cut into the desired size using Wirecut EDM Mitsubishi FX Series Machine in the presence of dielectric fluid (deionized water) with addition of anti rust agent liquid to reduce the surface rust. The kerf is measured using the Infinite Focus Alicona Machine as the sum of the wire diameter and twice wire workpiece gap. The kerf value was expressed in three different spot and each spot will give ten readings, the average of these reading will be taken as kerf width. The material removal rate (MRR) will be calculated using equation (1) this equation has been used by this researcher [15]. MRR = F D w H (1) Where F is the machine feed rate [mm/min], D w is wire diameter [mm] and H is piecework thickness [mm] and MRR is material removal rate [mm 3 /min]. After machining, surface roughness was measured using an Infinite Focus Alicona Machine on each piece work three times for achieving more accuracy and, subsequently, the average of it was selected (Figure 1). Stereo Zoom Microscope is used to see the macrostructure of machined surface (topography view). The results obtained will be represented in graphs and figures subsequently will be discussed. Fig. 1. Measurement of kerf width and surface roughness 3. Results and Analysis 3.1. Kerf Width Figure 2 shows that as the machine feed rate increases, the kerf widh decreases. Experiment with lower feed rate gives bigger width. K. P. Somashekar et al. [16] does not recommend the usage of high feed rate since it caused higher inaccuracies in the kerf width. Nihat Tosun et al. [17] proved that open circuit voltage and pulse duration were highly effective parameters on both the kerf and the MRR. It was found that open circuit voltage was about three times more important than the second ranking factor (pulse duration) for controlling the kerf.

4 Aniza Alias et al. / Procedia Engineering 41 ( 2012 ) Fig. 2. Result on kerf width at different machine feed rate 3.2. Material Removal Rate (MRR) It was found that with the increasing of machine feed rate, the MRR will increases simultaneously as shown in Figure 3. This result shows the same pattern with K. P. Somashekar et al. [16]. From the examination of the contour plot, it is noticed that MRR increases with increase in feed rate. Theoretically, material erosion is influenced by the spark energy. As feed rate increase; MRR also increases till it reaches optimum. The MRR decreased with the decreasing of machine feed rate. The results from Nihat Tosun et al. [17] verified that open circuit voltage was about three times more important than the open circuit voltage for controlling the MRR was about six times more important than the second ranking factor (pulse duration). MRR were found as open circuit voltage and pulse duration, whereas wire speed and dielectric flushing pressure were less effective factors. Fig. 3. Result on material removal rate at different machine feed rate 3.3. Surface Roughness (Ra) Surface roughness (Ra) is an element in measuring surface quality. It is one of the important factor in machining because it can predict the performance. Figure 4 enlightens that smoother surface can be obtained with low setting of machine feed rate. P.S. Rao et. al. [15] mentioned that, wire tension and spark gap voltage are observed as significant parameters in obtaining better surface finish. This is due to the increase of wire tension that reduces its vibration and improves the surface quality of the machined part. The increase of voltage means that the electric field becomes stronger and the spark discharge

1810 Aniza Alias et al. / Procedia Engineering 41 ( 2012 ) 1806 1811 takes place more easily under the same gap and a coarse surface is always obtained. Suleiman Abdulkareem et al.

) workpiece. Fig. 4. Result on surface roughness at different machine feed rate 3.4. Surface Topography Due to complicated machining process, machined surface topography can have complex and irregular condition.

$Amorim FL and Weingaertner WL [19] found that the fractal dimension of the multi-process is greater than the one of the single process, and the surface profile should be more complex and finer.$

5 1810 Aniza Alias et al. / Procedia Engineering 41 ( 2012 ) takes place more easily under the same gap and a coarse surface is always obtained. Suleiman Abdulkareem et al. [18] proved that wet WEDM can be used to improved surface roughness of titanium (Ti-6Al-4V) workpiece. Fig. 4. Result on surface roughness at different machine feed rate 3.4. Surface Topography Due to complicated machining process, machined surface topography can have complex and irregular condition. Figure 5 shows the surface topography of each experiment with 50 magnification using microscope. Amorim FL and Weingaertner WL [19] found that the fractal dimension of the multi-process is greater than the one of the single process, and the surface profile should be more complex and finer. They also define that roughness average (Ra) reflects the height information of the surface microscopic structure, and fractal dimension mainly shows the complex degree of surface topography, which reflects combined effect of surface spacing and the height and is independent of height characteristic and measurement scale. 2 mm/min 4 mm/min 6 mm/min Fig. 5. Illustration of topography view at different machine feed rate Conclusion In this paper, an effort was made to determine the important machining parameters for the performance of WEDM viz. kerf width, MRR and SR. The main goal is to find the best combination of machining parameters as known the cost and quality of WEDM which depends heavily on the process parameters. Machine feed rate have been proven to play an important role in this experimental work. Since the low kerf and the high MRR are equally important goals in WEDM, equal machine feed rate are recommended.

6 Aniza Alias et al. / Procedia Engineering 41 ( 2012 ) A.Alias et al / Procedia Engineering 00 (2012) Acknowledgements The authors would like to acknowledge the support from the management and staffs in Faculty of Mechanical Engineering, UiTM, Shah Alam, Malaysia, are thanked for their contribution in respected area. And all those who contributed directly or indirectly are thanked. References [1] Ho KH, Newman ST, Rahimifard S, Allen RD, 2004, State Of The Art In Wire Electrical Discharge Machining (WEDM). Int J Mach Tools Manuf 44: [2] D. Rakwal and E. Bamberg, 2009, Slicing, Cleaning and Kerf Analysis of Germanium Wafers Machined by Wire Electrical Discharge Machining, J. Mater. Process. Technol. 209(8), p [3] Sadiq MA, Rahman M, Lim HS, 2008, Study of WEDM parameter phenomena for micro fabrication. Int J Manuf TechnolnManag 13(2 4): [4] Miller SF, Kao C-C, Shih AJ, Qu J., 2005, Investigation of wire electrical discharge machining of thin cross-sections and compliant mechanisms. Int J Mach Tools Manuf 45: [5] Qu AJ Shih, RO S., 2002, Development of the cylindrical wire electrical discharge machining process: part І: concept, design and material removal rate. ASME J Manuf Sci Eng 124(3): [6] Qu AJ Shih, RO S., 2002, Development of the cylindrical wire electrical discharge machining process: part ІІ: surface integrity and roundness. J Manuf Sci Eng 124(4): [7] Bradley, E.F., 1988, Super alloys: A technical guide, ASM International. [8] Ezugwu, E.O., Da Silva, R.B., Bonney, J., Machado, A.R., 2005, Evaluation of the performance of CBN tools when turning Ti 6Al 4V alloy with high pressure coolant supplies, International Journal of Machine Tools and Manufacture, Vol. 45, pp [9] Pan, B., Kim, D.J., Kim, B.M., Dean, T.A., 2001, Incremental deformation and the forgeability of _ titanium aluminide, International Journal of Machine Tools and Manufacture, Vol. 41, pp [10] G. Lütjering, J.C. Williams, 2007, Titanium. Springer [11] E. Ezugwu, Z. Wang, 1997, Titanium alloys and their machinability a review, J. Mater. Process. Technol. vol. 68, pp , [12] M. Rahman, Y.S. Wong, A.R. Zareena, 2003, Machinability of titanium alloys, JSME Int. J. Series C46, pp , [13] S. Sarkar, M. Sekh, S. Mitra, B. Bhattacharyya, 2008, Modelling and Optimization of Wire Electrical Discharge Machining of K-TiAl in Trim Cutting Operation. Journal of Material Processing Technology 205: pg [14] R. Ramakrishnan, L. Karunamoorthy Modelling and Multi-Responses Optimization of Inconel 718 on Machining of CNC WEDM Processes. Journal of Material Processing Technology 207: Pg [15] Pujari Srinivasa Rao, Dr. Koona Ramji And Prof. Beela Satyanarayan,, 2010, A Prediction of Material removal rate for Aluminum BIS Alloy in wire-cut EDM, International Journal of Engineering Science and Technology Vol. 2 (12) [16] Kodalagara Puttanarasaiah Somashekhar & Nottath Ramachandran & Jose Mathew, 2010, Material removal characteristics of microslot (kerf) geometry in μ-wedm on aluminium Int J Adv Manuf Technol 51: [17] Nihat Tosun, Can Cogun and Gul Tosun, 2004, A study on kerf and material removal rate in wire electrical discharge machining based on Taguchi method [18] M. Reza, Soleymani Yazdi, Hoseyn, Dehghan and Hod, Amini, 2010, Modeling and Analysis of Process Parameters on State Variables in WEDM of TiB2 Nanocomposite Ceramic Applied Mechanics and Materials Vols pp [19] Amorim FL, Weingaertner WL, 2005, The influence of generator actuation mode and process parameters on the performance of finish EDM of tool steel. J Mater Process Technol 166: [20] Liao YS, Huang JT, Chen YH, 2004, A study to achieve a fine surface in wire-edm. J Mater Process Technol 149(1 3): [21] Yan MT, Lai YP, 2007, Surface quality improvement of wire- EDM using a fine-finish power supply. Int J Mach Tools Manuf 47(11): [22] Lei Geng, Huayan Zhong, 2010, Evaluation of WEDM Surface Quality Advanced Materials Research Vols pp

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