Optimization of machining parameters of drilling process in Magnesium alloy AZ31 A. Saravakumar 1, P. Sureshkumar 2, N. Balaji 3, R. Gokulnath 3, V. Mathavaram 3 1 Associate Professor, 2 Assistant Professor, 3 UG Scholar Department of Mechanical Engineering, KPR Institute of Engineering and Technology Coimbatore 641047, Tamilnadu, India. Abstract---The present research work deals with the effect of machining parameters such as drill diameter, spindle speed and cutting feed is investigated on the drilling ofmagnesium AZ31 alloy. Optimization of the machining parameters on magnesium alloy is necessary to avoid ignition of chips. This experiment is conducted based on L27 orthogonal array of Taguchi method to find the optimum drilling parameters and analysis of variance (ANOVA) is performed to analyse the influence of parameters on the surface roughness during drilling process on magnesium alloy. It is concluded that the surface roughness increases with the corresponding increase in the cutting feed and decrease in the spindle speed. Keywords--- Drilling, Magnesium alloy, Taguchi, ANOVA. I.INTRODUCTION Magnesium alloys, a light wright structural material has many advantages such as high stiffness-to-weight ratio and high strength-to-weight ratio and it is also called as green metal material in 21 st century. It is used in various fields such as construction of the body of electronic appliances along with computer and mobile phone, some spare parts of automobiles and also used in wide range of aerospace applications. In this scenario it is important to develop magnesium materials for its wide usage in automobile and aerospace application.liwei Lu et al [1] investigated the effect of cutting parameters on AZ31 alloy and observed that the roughness reduces with the increase of cutting speed and increases with the increase of depth of cut and feed rate. Drilling is one of the most important machining process and in fact it is not considered as a crucial factor to influence the quality of machine parts with magnesium alloys which is having a good machinability.whilecuttingisaverycostlyaffairwithsolidcarbideandevery breakage willprovetobeverycostlyon productivity.kwozong Chong and Teng Shih Shih [2] found that during drilling the hole produces twinning surface. This existence of twinning layer on the vicinity of the machined AZ61A is mainly induced by the compressive shear stress from the thrust force and from the chisel action of cutting and also found that using point angle 55 0 maintains surface roughness and also generates an ideal microstructure (the smallest extent of deformation of twinning layer). In this project Taguchi method was used for analysis. Genichi Taguchi developed this statistical method to improve the quality of products. This process has three stages namely system design, manufacturing design and tolerance design. Parameter design is used in this study, once the concept is established. The nominal values of the various parameters need to be set for the parameters. The experimental studies are done in the machines and the optimum parameters of machining is to be found. The surface roughness of the machined component is observed during this research.balaji et al [3] with the help of Taguchi and ANOVA analysis found the optimum levels of cutting parameters for surface roughness as 25 degree of helix angle, 12mm/min feed rate and 800rpm spindle speed.palanisamyshanmughasundaram and RamanathamSubramanian [4] applied L27 orthogonal array of Taguchi method and analysis of variance for investigating the cutting parameters on the exit burr height in drilling of Al-Gr composite and found that the optimum parameters for minimum exit burr height were feed(0.06mm/rev), spindle ISSN: 2348 8360 www.internationaljournalssrg.org Page 41
speed(600rpm), step angle(40 o ) and step size(1mm).arshad Noor Siddiquee et al [5] applied Taguchi method for optimization of process parameters during deep drilling operation and the improvement of surface roughness from initial cutting parameter to the optimal cutting parameters is about 131%. II. EXPERIMENTAL PROCEDURE A numerically controlled vertical milling machine is used in this study, Fig. 1. The sample material used is AZ31(3.5% Al, 1.4% Zn), it is prepared from an extruded rod, 50mm in diameter and each sample is 10mm in thickness. The cylindrical specimen was fixed on the pallet of the numerically controlled vertical milling machine through a clamp and the holes are drilled at different drilling parameters. Surface roughness of each drilled holes was measured using surface roughness tester and microstructure at the subsurface of the drilled holes is observed by optical microscope. Fig 1: Vertical Milling Machine ISSN: 2348 8360 www.internationaljournalssrg.org Page 42
Fig 2: Carbide Drill Bits Three standard twist drill bits (fig 2) made of carbide and different diameters of 6mm, 8mm and 10mm were used to drill holes in the samples of cylindrical magnesium alloy specimen. Three specimens were taken for the test. The first experiment was done using 6mm carbide drill bit to drill 9 holes of different parameter (feed 0.5, 1, 1.5mm/min and cutting speed 800, 1600, 2400 rpm). Similarly, second and third experiment was conducted using 8 and 10mm carbide drill bits. In total 27 holes were drilled with different parameters. Analysis of the surface roughness values was done using Minitab software as per L27 array Taguchi method. The cutting parameters and levels are tabulated in table1. Table 1: Cutting parameters and levels Parameters Unit Level 1 Level 2 Level 3 Diameter Mm 6 8 10 Spindle speed Rpm 800 1600 2400 Feed rate mm/min 0.5 1 1.5 III. RESULT AND DISCUSSION Considering the process parameters and its effects on the surface roughness, drilling process has been studied through: (i) Main effect plots, (ii) Response table, (iii) Analysis of Variance (ANOVA) technique based on Taguchi method L27 Orthogonal Array based on smaller the better concept. A. Surface Roughness Surface roughness values for the drilled surface were measured by using the surface roughness tester. In this experiment, the probe of the tester was made to get in contact with the drilled surface for few seconds and the surface roughness values is show in the display. Surface roughness is measured in order to find the finely spaced irregularities. For each drilled holes, the measurement is taken at three different locations on the drilled surface in order to obtain the absolute surface finish values. The average value of these three surface finish value is taken and tabulated and analysed with the help of Minitab 15 statistical software. Table 2 shows the calculated average surface roughness value. Table 2. Experimental Results Run no. Diameter(mm) Speed(rpm) Feed(mm/min) Surface roughness(µm) 1 10 800 0.5 0.988 2 10 800 1 1.023 3 10 800 1.5 1.236 4 10 1600 0.5 0.724 5 10 1600 1 0.843 6 10 1600 1.5 0.858 ISSN: 2348 8360 www.internationaljournalssrg.org Page 43
7 10 2400 0.5 0.568 8 10 2400 1 0.719 9 10 2400 1.5 0.77 10 8 800 0.5 0.662 11 8 800 1 0.784 12 8 800 1.5 0.869 13 8 1600 0.5 0.595 14 8 1600 1 0.737 15 8 1600 1.5 0.764 16 8 2400 0.5 0.547 17 8 2400 1 0.622 18 8 2400 1.5 0.674 19 6 800 0.5 0.471 20 6 800 1 0.523 21 6 800 1.5 0.566 22 6 1600 0.5 0.454 23 6 1600 1 0.495 24 6 1600 1.5 0.524 25 6 2400 0.5 0.422 26 6 2400 1 0.467 27 6 2400 1.5 0.475 B. Effect of process parameters The Main effect plots for Means show the effects of the process parameters and the levels on to the surface roughness. Figure 3 shows the main effect plots for the means. It is observed that better surface finish is obtained at smaller diameter (6mm), higher spindle speed (2400rpm) and lower feed rate (0.5mm/min). It is also noted that the surface roughness increase with the increase in the diameter of the drill bit, decrease in the spindle speed and increase in the feed rate. Figure 4 shows the residual plots of surface roughness values are scattered randomly. ISSN: 2348 8360 www.internationaljournalssrg.org Page 44
Frequency Percent Mean of Means SSRG International Journal of Mechanical Engineering (ICET 17) - Special Issue - March 2017 Main Effects Plot for Means Data Means 0.9 Diameter Speed 0.8 0.7 0.6 0.5 6 8 10 800 1600 2400 0.9 Feed 0.8 0.7 0.6 0.5 0.5 1.0 1.5 Fig 2: Main Effect Plot for Means Plots for Means 99 90 Normal Probability Plot 0.02 Versus Fits 50 10 0.00-0.02 1-0.050-0.025 0.000 0.025 0.050-0.04 0.4 0.6 0.8 Fitted Value 1.0 1.2 Histogram Versus Order 8 0.02 6 4 0.00 2-0.02 0-0.04-0.03-0.02-0.01 0.00 0.01 0.02 0.03-0.04 2 4 6 8 10 12 14 16 18 20 Observation Order 22 24 26 Fig 4: Plot for Means ISSN: 2348 8360 www.internationaljournalssrg.org Page 45
Table 3: ANOVA Table Sources DF Seq SS Adj SS Adj MS F P Pc Diameter 2 0.61949 0.619493 0.309746 329.44 0 59.889 Speed 2 0.19472 0.19472 0.09736 103.55 0 18.824 Feed 2 0.09585 0.95855 0.047927 50.97 0 9.266 Diameter*Speed 4 0.09637 0.096372 0.024093 25062 0 9.316 Diameter*Feed 4 0.013 0.013003 0.003251 3046 0.064 1.256 Speed*Feed 4 0.00743 0.007425 0.001856 1.97 0.192 0.718 Error 8 0.00752 0.007522 0.00094 0.726 Total 26 1.03439 99.995 Table 4: Response table for surface roughness Level Diameter Speed Feed 1 0.4886 0.7913 0.6034 2 0.6949 0.666 0.6903 3 0.8588 0.5849 0.7484 Delta 0.3702 0.2064 0.145 Rank 1 2 3 From the ANOVA table (Table 3) for surface roughness it is observed that the diameter has the maximum influence on surface roughness with 59.88% of contribution, followed by spindle speed with 18.82 % contribution and feed rate with 9.26 % contribution. Other interactions have small effect on surface roughness and the residual errors are only 0.72%. From the analysis of mean, it is concluded that diameter of the drill bit has the maximum percentage of contribution to surface roughness, followed by spindle speed. When compared to feed rate, spindle speed is the most influencing parameter which affects the surface roughness significantly. From response table (Table 4) it is observed that the diameter influences a lot on the surface roughness of the holes than the other two parameters. From the response table and main effect plot it concluded that the optimum conditions are diameter of the drill bit (6mm), ISSN: 2348 8360 www.internationaljournalssrg.org Page 46
spindle speed (2400rpm) and feed rate (0.5mm/min). From the response table (Table 4) it is observed that the ranks 1,2 and 3 were given to diameter of the drill bit, spindle speed and feed rate respectively. The table values show the parameters which has the effect on surface roughness. IV. CONCLUSION This work shows the application of Taguchi method in the analysis of machining process parameters in drilling process. The following conclusions are drawn based on the experimental results of this study: i.the experimental results show that diameter of the drill bit is the major influencing parameter among the three controllable factors on surface roughness. ii. Minimum surface roughness obtained at optimum level: diameter of drill bit 6mm, spindle speed 2400rpm and feed rate 0.5mm/min. iii. The drilling parameters studies showed that spindle speed influenced more on surface roughness than feed rate. REFERENCES [1] Liwei Lu, Shaohua Hu, Longfei Liu and Zhenru Yin, High speed cutting of AZ31 magnesium alloy, Journal of Magnesium and Alloys Vol. 4(2016), pp. 128-134. [2] KwoZong Chong and Teng Shih Shih, Optimizing drilling condition for AZ61A Magnesium alloy, Materials Transactions, Vol. 43, No. 8 (2002) pp. 2148-2156. [3] M. Balaji, B.S.N. Murthy, N. Mohan Rao, Optimization of Cutting Parameters in Drilling of AISI 304 Stainless Steel Using Taguchi and ANOVA, Procedia Technology, Vol. 25 (2016), pp. 1106-1113. [4] PalanisamyShanmughasundaram and Ramanatham Subramanian, Study of parametric optimization of burr formation in step drilling of eutectic Al-Si alloy-gr composites, Journal of Material Research and Technology, 2014, 3(2), pp. 150-157. [5] Arshad Noor SiddiqueeZahid A. Khan, PankulGoel, MukeshKumar,Gaurav Agarwal, Noor Zaman Khan, Optimization of Deep Drilling Process Parameters ofaisi 321 Steel using Taguchi MethodProcedia Materials Science, Vol. 6 ( 2014 ), pp. 1217 1225 ISSN: 2348 8360 www.internationaljournalssrg.org Page 47