Journal of Engineering, Computers & Applied Sciences (JEC&AS) ISSN No: Volume 2, No.6, June 2013

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1 ISSN No: Volume, No.6, June Optimization of Machining Parameters of Titanium Alloy for Tool Life Kapil Kumar Chauhan, Asst. Professor, Mechanical Engineering Department, Graphic Era University Dehradun, Uttarakhand Dinesh Kumar Chauhan, Post Graduate Student, Mechanical Engineering Department, Bhagwant Institute of Technology, Muzaffarnagar, Uttar Pradesh ABSTRACT High speed machining of highly reactive material like titanium and its alloys is still far away uncertain. For this reason, it is wiser to study the optimization of Machining parameters under transient cutting speed before advancing to high speed machining. This paper presents the influence of machining parameters like coolant flow rate, cutting speed on Tool life of Titanium alloy during machining. Machining process is carried out in dry or nearly dry condition using Physical Vapor Disposition (PVD) coated cemented carbide tools. For near dry machining, two levels of coolant flow rate of 5 and ml/h were investigated. A plan of experiments based on Taguchi technique has been used to acquire the data. An Orthogonal array and signal to noise (S/N) ratio are employed to investigate the machining characteristics of titanium alloy & optimize the machining parameters. In optimization technique, Taguchi method is used for optimization for Variable parameters coolant flow rate (, 5& ml/hr), cutting speed (, 5 & 5m/min), feed rate (.,.5,.5mm/tooth) and depth of cut (,.5 &.5 mm). Finally Minitab 5, a comprehensive DOE tool is used for multilevel factorial screening designs to help you find the critical factors that lead to breakthrough improvements Keywords: - Minitab 5, Optimization, Orthogonal array, PVD Cemented carbide tool, Titanium alloy, Tool life, Taguchi method, Signal-to-Noise Ratio(S/N). Introduction Titanium and its alloys are widely used in aerospace industries due to attractive characteristics of the material, they offers a combination of high strength, light weight, formability and corrosion resistance which have made it a world standard in aerospace applications. However, these materials have been classified as difficult-to machine material because of their high temperature strength, low thermal conductivity, chemical reactivity and relatively low modulus of elasticity []. Furthermore these materials can catch fire at temperature 6 C and the only material can burn in pure nitrogen []. In machining process, most of the mechanical energy used to remove material becomes heat. This heat generates high temperature in the cutting region. The higher the cutting speed, the faster the heat generation and higher temperature resulted. The new challenge in machining is to use high cutting speed in order to increase the productivity. This is the main reason for rapid tool wear. For titanium and its alloy, this problem is more severe due to their low thermal conductivity. 8% of the heat generated in the cutting region goes to the cutting tool and cause wear []. So it is convenient to use transient cutting speed for machining the highly reactive material like titanium alloy. Another Conventional method used to reduce this tool wear is by using cutting fluid. This cutting fluid acts as lubricant and coolant as well during the machining process. Usage of cutting fluid can increase the cutting speed up to % without affecting the tool life. However the usage of cutting fluid has negative effect to the economy, environment and health [4]. Total elimination of cutting fluid seems to be not promising due the unsatisfactory tool life and poor surface finish [5]. This rapid tool wears not only gives higher surface roughness value, but also higher micro hardness and major microstructure alteration [6]. So it is better to optimize the variable parameters (coolant flow rate, cutting speed, feed rate and depth of cut) for tool life to increase the productivity at good surface finish. For optimization Taguchi method is used. The Taguchi method is a well-known technique that provides a systematic and efficient methodology for process optimization and this is a powerful tool for the design of high quality systems. Taguchi approach to design of experiments in easy to adopt and apply for users with limited knowledge of statistics, hence gained wide popularity in the engineering and scientific community. This is an engineering methodology for obtaining product and process condition, which are minimally sensitive to the various causes of variation, and which produce high-quality products with low development and manufacturing costs. Signal to noise 57

2 ISSN No: Volume, No.6, June ratio and orthogonal array are two major tools used in design. The S/N ratio characteristics can be divided into three categories when the characteristic is continuous a) Nominal is the best b) Smaller the better c) Larger is better characteristics. For the maximum Tool life, the solution is Larger is better and S/N ratio is determined according to the following equation: S/N = - log { } Where, S/N = Signal to Noise Ratio, n = No. of Measurements, y = Measured Value The influence of each control factor can be more clearly presented with response graphs. Optimal cutting conditions of control factors can be very easily determined from S/N response graphs, too. Parameters design is the key step in Taguchi method to achieve reliable results without increasing the experimental costs. Methodology. Work Piece Among the titanium alloy used in aerospace industries, the Titanium alloy from alpha-beta group Ti-6Al-4V is the most widely used. This material is selected for this experiment. The dimensions of the Ti-6Al-4V test piece are xx6 mm. The composition (Weight %) and the mechanical properties of this material are shown in Tables and respectively. Table Composition (Weight %) of Work Piece Serial No. Content Weight % O - H.5 N. 4 C.5 5 Fe.9 6 V Al Ti Balance Table Mechanical Properties of Work Piece Serial Mechanical Property value No.. Tensile strength (MPa) 99. Yield Strength (MPa) 8. Elongation 4 4. Modulus of Elasticity 4 (GPa) 5. Hardness (HRC) 6. Cutting Tool Material PVD coated cemented carbide Tool was used in this experiment. The composition (Weight %), Physical & mechanical properties and Geometry of this Tool are shown in Tables, 4 and 5 respectively. Table Composition Serial No. Content Weight % WC 87 Co Table 4 Physical and Mechanical Properties Serial No. Properties Value Particle size.8µm Hardness 47 Hv Density 4.5 g/cm 4 Modulus of 58 GPa Elasticity 5 Coefficient of 5.5 x -6 /K thermal Expansion Table 5 Geometry of Cutting Tool Serial No. Angle Value Cutting Rake -4 o - o Axial Rake +6 o Radial Rake -4 o - o. Cutting Fluid Water immiscible cutting fluid was used during this experiment. However, this coolant is miscible with solvent or mineral oil. Desired coolant flow rate was achieved by regulating the supplied air pressure and the 58

3 Journal of Engineering, Computers & Applied Sciences (JEC&AS) ISSN No: Volume, No.6, June opening of nozzle. Mechanical properties of the cutting fluid are shown in Table 6 Table 6 Mechanical properties of cutting fluid Serial No. Properties Value Design Of Experiment All the machining tests were carried out on -axis CNCC milling machine. Type of cutting used in this experiment is climb milling shown in figure. Design of experiment was multilevel factorial design, used in this experiment. Summary of the Design of Experiment is shown in Table 7. Figure Climb Milling Specific.874 g/cm Gravity DIN Viscosity. mm /s DIN 5 56 Flash Point 78 o C ISO 59 Pour Point - o C ISO 6 Table 7 Design of Experiment Seri Factors /Level al No. A- Coolant flow rate, Q (ml/h) 5 B- Cutting speed, V c (m/min) 5 5 C- Feed rate, FR (mm/tooth) D Axial Depth of cut (DOC), a - mm.5.5 Machining was stop at various time intervals to measure the tool wear progressively. Measurements of tool wear were stopped, when either one of these criteria was obtained: - Thee flank wear reached. mm - Catastrophic tool failure - Machining time reached minutes 5. Taguchi Orthogonal Array If there is an experiment having factors which have threee values, then total number of experiment is 7. Thenn results of alll experiment will give accurate results. In comparison to above method the Taguchi orthogonal array make list of nine experiments in a particular order which cover all factors. Those nine experiments will give 99.96% accurate result. By using this method number of experiments reduced to 9 instead of 77 with almost same accuracy. Taguchi Orthogonal arrayy is shown by Table 8 Table 8 Taguchi Orthogonal Array Serial No. Coolantt Flow Rate Cutting Speed Feed Rate Depth of cut Observation Totall nine experiments are performed to find Tool life which is show in table 9. Table 9 Observation Seriall Coolant Cutting No. Flow Rate Speed (ml/hr) (m/min) Feed Rate mm/tooth) Depth of Tool LifeL cut (min) (mm)

4 ISSN No: Volume, No.6, June Results & Discussion Calculations After finding all the observation as given in Table 9, S/N ratio and Means are calculated and various graph for analysis is drawn by using Minitab 5 software. The S/N ratioo for tool life is calculated on Minitab 5 Software using Taguchi Method. The steps used are as follows: Starting Minitab 5:- To start Minitab, click shortcut of Minitab on Desktop of computer. A window is opened in computer as shown in Figure:- Design of Orthogonal Array First Taguchi Orthogonal Array is designed in Minitab5 to calculate S/N ratio and Means which steps is given below: 6

5 ISSN No: Volume, No.6, June Taguchi orthogonal Array Putting value in the Taguchi Orthogonal Array 6

6 ISSN No: Volume, No.6, June Analyze Taguchi Design 6

7 ISSN No: Volume, No.6, June Results Taguchi method stresses the importance of studying the response variation using the signal to noise (S/N) ratio, resulting in minimization of quality characteristic variation due to uncontrollable parameter. The tool life was considered as the quality characteristic with the concept of "the larger-the-better". The S/N ratio for the larger-the-better is: S/N = - log { } Eqn. Where n is the number of measurements in a trial/row, in this case, n= and y is the measured value in a run/row. Thee S/N ratio values are calculated by taking into consideration Eqn. with the help of software Minitab 5. The tool life values measured from the experiments and d their corresponding S/N ratio values are listed in Table. Table Result Serial Coolant No. Flow Rate (ml/hr) Cutting Speed (m/min) Feed Rate (mm/tooth) Depth off cut (mm) Tool Life (min) S/N Ratio Mean Analysis and Discussion 6

8 ISSN No: Volume, No.6, June Regardless of the category of the performance characteristics, a greater S/N value corresponds to a better performance. Therefore, the optimal level of the machining parameters is the level with the greatest value. Coolant Flow Rate The effect of parameters coolant flow rate on the tool life values is shown above figure for S/N ratio. Its effect is increasing with increase in coolant flow rate. So the optimum coolant flow rate is level i.e. ml/hr. Cutting speed The effect of parameters cutting speed on the tool life values is shown above figure for S/N ratio. Its effect is decreasing with increase in cutting speed. So the optimum cutting speed is level i.e. m/min. Feed Rate The effect of parameters feed rate on the tool life values is shown above figure for S/N ratio. Its effect is decreasing with increase in feed rate. So the optimum feed rate is level i.e.. mm/tooth 4. Depth of cut The effect of parameters depth of cut on the tool life values is shown above figure for S/N ratio. Its effect is decreasing with increase in depth of cut. So the optimum value is level i.e.. mm. Higher cutting speed results in shorter tool life. But at higherr feed rate and depth of cut, effect of cutting speed is less significant. This is due to fracture failure and iss more important than gradual wear when high feed rate and high depth of cut are applied. Longer tool life, when higher amount of coolant is applied, only occurss at cutting of 5 m/min. At the speed of m/min, dry machining gives better tool life. Shorter tool lifee under MQL 5 ml/h is observed due too the chemical wear [4]. The wear increase drastically when the coating material had been eliminated. Under MQL ml/h, the effect of wear is less because sufficient amount of coolant is available to give the cooling effect. Contrary, for cuttingg speed 5 m/min, MQL ml/h is less efficient as compared to MQL 5 ml/h. This is due to the bigger size of mist particles that cannot penetrate in to the cutting zone. The penetration of this particle is hindered by the centrifugal force created by the rotating tool. 64

9 ISSN No: Volume, No.6, June References [] E. O. Ezugwu, "Key improvements in the machining of difficult-to cut aerospace super alloys, "International Journal of Machine Tool and Manufacturer, pp. 5-67, 5. [] Anonymous, "Machining Titanium and its alloys," < accessed 4//6. [] E. O. Ezugwu, J. Booney, and Y. Yamane, "An overview of the machinability of earoengine alloys, "Journal of Materials Processing Technology, pp. -5,. [4]"Titanium," < accessed /6/. [5] N. R. Dhar, M. T. Ahmed, and S. Islam, "An experimental investigation on effect of minimum quantity lubrication in machining AISI 4 steel, "International Journal of Machine Tools and Manufacturer, pp , 7. [6] C. H. Che Haron, "Tool life and surface integrity in turning titanium alloy, "Journal of Materials Processing Technology, pp. - 7,. [7] S. Cardoso Santos, W. F. Sales, F. J. da Silva, S. D. Franco, and M. B. da Silva, "Tribological characterization of PVD coatings for cutting tools, "International Journal of Surface and Coating Technology, pp. 4-48,. [8] M. Sokovic, J. Kopac, L. A. Dobrzanski, and M. Adamiak, "Wear of PVD-coated solid carbide end mills in dry high-speed cutting, " Journal of Materials Processing Technology, pp. 4-46, 4. [9] M. Rahman, A. Senthil Kumar, and M.U. Salam, "Experimental evaluation on the effect of minimal quantities of lubricant in milling, "International Journal of Machine Tools and Manufacturer, pp ,. [] M. Rahman, Z. G. Wang, and Y. S. Wong, "High speed machining of Titanium alloys, "presented at International Conference on Manufacturing Science and Technology, Malaysia, 6. [] N. R. Dhar, M. Kamruzzaman, and M. Ahmed, "Effect of minimum quantity lubrication (MQL) on tool wear and surface roughness in turning AISI-44 steel, Journal of Materials Processing Technology, pp. 99-4, 6. ] L. N. Lopez de Lacalle, C. Angulo, A. Lamikiz, and J. A. Sanchez, "Experimental and numerical investigation of the effect of spray cutting fluids in high speed milling, "Journal of Materials Processing Technology, 5. [] M. Rahman, Z. G. Wang, and Y. S. Wong, "High speed machining of Titanium alloys, "presented at International Conference on Manufacturing Science and Technology, Malaysia, 6. [4] A. Bhattacharyya, Metal Cutting - Theory and practice. India,