Optimization of Machining Parameters for cutting temperature on turning of Niobium alloy C-103by using RSM

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1 Optimization of Machining Parameters for cutting temperature on turning of Niobium alloy C-103by using RSM 1 K. Someswara Rao, 2 C.S.P.Rao, 3 P.S.C.Bose 1,2,3 Department of Mechanical Engineering, NIT Warangal, Telangana, India. Abstract : Niobium based super alloys are an unusual class of metallic materials with an exceptional combination of high temperature strength, toughness, and resistance to degradation in corrosive or oxidizing environments. The focus of present work was to study the effect of cutting parameters speed, feed and depth of cut on the machinability of Niobium C-103 under dry machining condition using response surface methodology (RSM) 1. In present study various machinability models were developed. This machinability models defined a functional relationship between cutting variables and response (Cutting Temperature). Cutting levels for experimentation was selected based on the cutting insert manufacturer recommendations. The analysis shows that Cutting speed is the most evident factor for cutting temperature. Keywords : Super alloy, Dry Machining, Machinability, Cutting temperature, PVD coated tool, Response Surface Methodology(RSM). I. INTRODUCTION The requirement for high-performance, lightweight space propulsion systems has prompted rapid investigation of refractory metals that are capable of withstanding high stress levels at elevated temperatures, and also have a low ductile-to-brittle transition temperature for withstanding high frequency vibrations at cryogenic temperatures. The metals which demonstrate these requirements are the Niobium based alloys. C-103 Niobium alloy was selected to satisfy initial design requirements because of its excellent fabricability. C-103 Niobium alloy is considered the most "forgivable" Niobium alloy from the standpoint of welding and spinning. Hardware which has had as much as 600" of TIG weldments formed after welding and coating has withstood a 2T bend at -196 C (-320 F) after the unit had completed its duty cycle. This Niobium-Hafnium-Titanium alloy satisfies most rocket engine applications for temperatures up to 1482 C (2700 F) because of superior mechanical properties at all temperatures. The interior of a functioning gas turbine is a challenging environment where the temperatures and pressures can be well beyond the limits of conventional metals, and as designers continue to improve turbine efficiency so these testing conditions become ever more severe. Consequently, specially developed alloys are required for components exposed to the most demanding temperatures, or for items whose structural integrity is critical. Input Output Speed Feed Depth of Cut Niobium C-103 Machining Cutting Temperature Fig.1.Interrelations between the processing conditions and the output variables Response surface methodology (RSM) is a collection of mathematical and statistical techniques that are useful for the modeling and analysis of problems in which a response of interest is influenced by several variables and the objective is to optimize this responses. In many experimental conditions, it is possible to represent independent factors in quantitative form as given in Equation 1. Then these factors can be thought of as having a functional relationship with response as follows: 13

2 .1 This represents the relation between response Y and x1, x2 xk of k quantitative factors. The function Φ is called response surface or response function. The residual er measures the experimental errors 2. For a given set of independent variables, a characteristic surface is responded. When the mathematical form of Φ is not known, it can be approximated satisfactorily within the experimental region by a polynomial. II. APPARATUS 2.1. CNC Lathe: The Retrofitted VDF CNC lathe machine was used for experimental work. It is supported with spindle drive motor 12KW and 6000 Rpm maximum speed, distance between centers 100cm and feed 0.04 to 205mm.The CNC Lathe Machine as shown in figure below. Fig: 2.Heavy duty CNC Lathe 2.2. Work Material:Niobium alloy C-103 is a precipitation hardening, creep resisting Nickel-chromium-cobaltmolybdenum alloy developed by Rolls Royce. It is supplied in high temperature annealed condition and can service up to 950 degree centigrade. Table.1: Chemical composition of Niobium alloy C-103 Hf(%) Zr(%) Tantalum Nickel(%) Carbon(%) Oxygen(%) Niobium C balance 2.3. Cutting inserts and holder: In this experimental study PVD coated tools were used, as they are generally preferred material in such experiments. The inserts were manufactured by SANDVIK, with the ISO designation of TNMG MF, (Triangular inserts). A double clamp-type tool holder designated by ISO as DTGNL 2020 K16. It is fixed with the fixture that is fitted on the dynamometer and overhang is kept as low as possible to increase the rigidity of the setup. 2.4 Cutting condition: Since not much research work related to machining of Niobium alloy C-103 has been done far, so initial values of each independent parameter were selected based on tool manufacturer recommendations and machine tool capabilities. Table.2: Input parameters and their levels. Factor Units Low level (- 1) Centre level (0) 14 High level (+1) Speed m/min Feed mm/rev Depth of mm cut 2.5. Temperature measurement: Infrared thermometer Kiray 300 was used for temperature measurement while conducting the experiments. This is a thermometer used to diagnose, inspect and check any temperature measurements of little distant targets. The KIRAY 300 instrument has an internal memory which can save up to 100 measurements. Infrared thermometers can measure the surface temperature of an object. Its optic lens catches the energy emitted and reflected by the object.

3 This energy is collected and focused onto a detector. This information is displayed as temperature. The laser pointer is only used to aim at the target. Fig.3.Infrared thermometer Kiray 300 Fig. 4: Infrared thermometer III. RESULTS AND DISCUSSION 3.1 Effect of process variables on cutting temperature (CT) Table.3: ANOVA table for Response Surface Reduced 2FI Model for CT 15

4 3.2 Statistical Inferences The Model F-value of 4.63 implies the model is significant. There is only a 1.37% chance that a "Model F-Value" this large could occur due to noise. Values of "Prob > F" less than indicate model terms are significant. In this case A, BC is significant model terms. Values greater than indicate the model terms are not significant. If there are many insignificant model terms (not counting those required to support hierarchy), model reduction may improve your model. The "Lack of Fit F-value" of 2.56 implies the Lack of Fit is not significant relative to the pure error. There is a 18.95% chance that a "Lack of Fit F- value" this large could occur due to noise. Nonsignificant lack of fit is good -- we want the model to fit. The various R 2 statistics (i.e. R 2, adjusted R 2 (R 2 adj) and predicted R 2 (R 2 pred)) of the surface roughness are as follows. The value of R 2 = for surface roughness indicates that 56.96% of the total variations are explained by the model. The adjusted R 2 is a statistic that is adjusted for the size of the model; that is, the number of factors (terms). The value of the R 2 adj = indicates that 44.66% of the total variability is explained by the model after considering the significant factors. 3.4 Response Curves generated R 2 pred = is in fair agreement with the R 2 adj and shows that the model would be expected to explain 15.60% of the variability in new data (Montgomery, 2001). C.V. stands for the coefficient of variation of the model and it is the error expressed as a percentage of the mean ((S.D./Mean) 100). Lower value of the coefficient of variation (C.V. =13.64) indicates improved precision and reliability of the conducted experiments. "Adeq Precision" measures the signal to noise ratio. A ratio greater than 4 is desirable. Here ratio of indicates an adequate signal. This model can be used to navigate the design space. 3.3 Mathematical Model Generated After Regression Analysis The regression coefficients of the second order equation are obtained by using the experimental data. The regression equation for the surface roughness as a function of three input process variables was developed using experimental data and is given below. Final equation in terms of actual factors after eliminating insignificant terms: Temp = *v *f *d *f*d. Fig.5: Deviation from Reference Point 16

5 IV. CONCLUSION In this paper, the application of RSM on the Niobium alloy C-103 is carried out by turning with PVD coated insert tools. In addition, involves analysis of cutting temperature in turning operation on Niobium alloy C- 103 so as to investigate the influence of cutting parameters. The results of the research are as follows: 1) The cutting temperature CT fitted to the 2FI model in the given range of parameters. 2) Cutting speed is found to be main influencing factor on cutting temperature. 3) Optimum value of parameters to minimize the value of Cutting Temperature is Cutting speed =80.00m/min, Feed = 0.08 mm/rev & Depth of cut = 0.60 mm V. ACKNOWLEDGEMENTS 1. My Sincere thanks to my project guide Dr. C. S. P. Rao for his guidance to complete this project work. 2. I express my Warm thanks to Smt. O. Vijayalakshmi, RJD (Retd) and Mr. G. Gesudasan, Retd., Principal (Late) for their continuous support and guidance to complete this project work. 3. I would like to thank Dr. P. Ravi Kumar, HOD, Physical Education Dept. NITW and Dr. B. S. Anuradha for their moral support. 4. My sincere thanks to Smt. Jean Moore, Dr. Joseph Ravindra Duddu Mch(Neuro), and Sri. B. Krishna Murthy Garufor their financial support. Fig.6. Response of Cutting temperature with feed and speed REFERENCES [1] K. Someswara Rao, C.S.P.Rao and P.S.C.Bose,Optimization of Cutting parameters for cutting force on turning of niobium alloy c103 using response surface methodology, International Journal of Innovative science, Engineering & Technology june-2014, Page no: [2] Cochran and Cox, Experimental Design, 2 nd Edition. [3] Mikell P. Groover, Fundamentals of Modern Manufacturing, Pg , 4th Edition. [4] E.O. Ezugwaa, J. Bonney, Y.Yamane, An overview of the machinability of aeroengine alloys. Journal of materials processing technology 134 (2003), [5] Douglas Montgomer,Text book of Design and Analysis of Experiments. Pg No [6] Suleiman Abdulkareem, optimization of machining parameters during turning process, International Journal of Integrated Engineering, Vol. 3 No. 1 (2011) p [7] A. Devillez, F. Schneider, S. Dominiak, D. Dudzinski, D. Larrouquere, Cutting forces and wear in dry machining of Inconel 718 with coated carbide tools.wear 262 (2007) [8] Ashvin J, Optimisation of machining parameters for turning operations based on response surface methodology. Journal of the International Measurement Confederation (IMEKO), Measurement 46 (2013)