In this paper the performances, i.e. cutting force, moment and surface roughness, in the end milling of aluminum 6082-T6 with solid carbide end mill were measured and analyzed for different values of the cutting parameters: number of revolutions, feed rate and depth of cut. The cutting force and moment were measured using a Kistler piezoelectric dynamometer. Surface roughness was measured using a Mahr profilometer. The results were analyzed in the Minitab 17 software package, in order to determine the influence of the given factors on the performances and modeling of the milling process

Radovanović, Miroslav

Stanojković, Jelena

University of Niš: Facta Universitatis (E-Journals) / Универзитет у Нишу

FACTA UNIVERSITATIS  Series: Mechanical Engineering DOI: 10.22190/FUME180220002S Original scientific paper ∗INFLUENCE OF THE CUTTING PARAMETERS ON FORCE, MOMENT AND SURFACE ROUGHNESS IN THE END MILLING OF ALUMINUM 6082-T6  Jelena Stanojković, Miroslav Radovanović Faculty of Mechanical Engineering, University of Niš, Serbia Abstract. In this paper the performances, i.e. cutting force, moment and surface roughness, in the end milling of aluminum 6082-T6 with solid carbide end mill were measured and analyzed for different values of the cutting parameters: number of revolutions, feed rate and depth of cut. The cutting force and moment were measured using a Kistler piezoelectric dynamometer. Surface roughness was measured using a Mahr profilometer. The results were analyzed in the Minitab 17 software package, in order to determine the influence of the given factors on the performances and modeling of the milling process. Key Words: Cutting Force, Moment, Surface Roughness, Aluminum 1. INTRODUCTION  The cutting force, moment and surface roughness are the most important indicators of machinability of materials and are very significant for the theory of cutting processes. By separating the cutting layer from the machining surface, the cutting edge of the cutting tool encounters the force. This force removes a layer of material and separates it from the workpiece in the form of chips. Depending on the machining conditions, the magnitude of force can vary widely. The force is the main indicator of wear control, the quality of the machined part, and the shape of chips and vibrations. Knowing the cutting force enables one, among other things, to determine the energy balance of the machine tool, do the calculation and dimensioning of the elements of the kinematic system of machine tool, do the calculation and dimensioning of the cutting tool, optimize the machining process and enhance the efficiency of the process based on the calculation of the optimal values of the cutting parameters [1]. The force can be determined by measuring the components by the dynamometer.                                                          Received February 20, 2018 / Accepted November 20, 2018 Corresponding author: Jelena Stanojković  Faculty of Mechanical Engineering, University of Niš, A. Medvedeva 14, 18000 Niš, Serbia E-mail: jstanojkovic@masfak.ni.ac.rs 2 J. STANOJKOVIĆ, M. RADOVANOVIĆ The force components in the end milling process can be decomposed into [2]: • Fc-cutting (tangential) force, • Ff-feed (radial) force, and • Fp-thrust (axial) force. The machined surface quality is evaluated by surface roughness of the machined part and it is one of the most significant product quality characteristics [3, 4]. Surface roughness depends on the cutting conditions, especially the form of cutting tools, tool wear, deposits, vibration, etc. The basic parameters for monitoring surface roughness are: • Ra-arithmetic average of the absolute values, • Rz-medium unevenness depth, and • Rmax-maximum unevenness depth. Milling achieves surface roughness from N5 to N12 with the arithmetic average of absolute values Ra of 0.4 to 50 μm, respectively. The experimental measurement of cutting force and surface roughness in the milling process has been investigated by a large number of researchers and so has the application of analytical methods for modeling. One of the most important analytical models of the cutting force was created by Kienzle and Victor [5] in the 1950s. Ganesh Babu [6] investigated the effects of the cutting parameters (cutting speed, feed rate and depth of cut) on the cutting force during end milling of AlSiC metal composite material using the Response Surface Methodology (RSM). The experiment was conducted using a four teeth high-speed steel end milling cutter with 10 mm in diameter on the vertical milling machine. The cutting forces were measured with a Kistler piezoelectric dynamometer, type 9257B. The cutting forces increased when the depth of cut increased. Tsai [7] investigated the influence of the feed per tooth and the tool diameter on the cutting force in milling aluminum 6060-T6. The experiment was conducted using a carbide end milling cutter with two teeth and with diameters of 12, 16, and 20 mm, the spindle speed of 1000 rev/min and the depth of cut of 1 mm, while the feed rate was varied with values of 200, 260, 300, 360 and 400 mm/min. The cutting forces were measured with a Kistler piezoelectric dynamometer, type 9257B. The cutting forces were simulated by the Recursive Least Square (RLS) method and compared with the experimental values. Thamban [8] investigated the machining parameters (spindle speed, feed rate and depth of cut) during end milling aluminum 6061-T6 with coated tungsten carbide and diamond coated end milling cutter with 10mm in diameter. All the components of the cutting forces were measured with a Kistler piezoelectric dynamometer, type 9257B. The cutting force was observed to be increasing with depth and feed rate during the end milling for both the cutting tools (coated and uncoated). Turgut [9] investigated the effect of machining parameters (cutting speed, feed rate and depth of cut) on the cutting force and surface roughness in the face milling operation of AlSiC metal matrix composites. The cutting force and surface roughness were measured at cutting speeds of 300, 350, 400 and 450 m/min, feed per tooth of 0.1, 0.15 and 0.20 mm/tooth and depth of cut of 0.5 and 1 mm. The experiment was conducted using coated and uncoated milling cutters of 32 mm in diameter on the vertical machining center Johnford VMC-850 without using coolant. The cutting forces were measured with a Kistler piezoelectric dynamometer, type 9257B. Increasing the feed per tooth and depth of cut increased the cutting force for all the cutting conditions, but increasing cutting speed decreased the cutting force. The best results of the cutting force were obtained with the cutting speed of 400 m/min and the feed rate of 0.1mm/tooth. Jeykumar [10] investigated the influence of spindle speed, feed  Influence of Cutting Parameters on Force, Moment and Surface Roughness in End Milling 3  rate and depth of cut on the cutting force, tool wear and surface roughness in the end milling operation of Al6061/SiC using the Response Surface Methodology. The experiment was conducted using a milling cutter with indexable inserts made of tungsten carbide on the milling machine HMT-FNIU. The cutting forces were measured using a Kistler piezoelectric dynamometer, type 5070. The experimental results were compared with the mathematical model developed using the Response Surface Methodology.  The objective of this study is to determine the influence of the factors (spindle speed, feed rate and depth of cut) on the performances (cutting force, moment and surface roughness) in the end milling of aluminum alloy 6082-T6. The obtained mathematical model facilitates planning the milling process. 2. EXPERIMENTAL STUDY In the experimental measurements of the force, moment and surface roughness in the end milling samples of aluminum alloy 6082-T6 were used, with the following dimensions of the workpiece: 50x30x400 mm. The chemical composition of the aluminum alloy 6082-T6 is given in Table 1. Table 1 Chemical composition of Al 6082-T6 Chemical elements Composition [%] Al 95.2-98.3 Cr 0.25 Cu 0.1 Fe 0.5 Mg 0.6-1.2 Mn 0.4-1.0 Si 0.7-1.3 Ti 0.1 Zn 0.2 Others 0.15  The cutting tool that was used in the experiment was solid carbide end mill JS413160D2SZ3.0, manufactured by SECO, Fig 1. The geometry of the end milling cutter is given in Table 2 [11].  Fig. 1 Solid carbide end mill SECO 4 J. STANOJKOVIĆ, M. RADOVANOVIĆ Table 2 Cutting geometry of solid carbide end mill  Diameter-Dc[mm] 16 Max depth of cut-ap [mm] 32 Diameter of tool shrank-dm [mm] 16 Length of cutting tool- l2 [mm] 100 Number of teeth- zn 3 Helix angle-ω [°] 40 Cutting tool edge angle-κ [°] 90 Rake angle-ε [°] 20  For design of the experiment the selected factors of the milling process were spindle speed (n), feed rate (Vf) and depth of cut (ap). They were the main factors that influence the cutting force, moment and surface roughness. The factors were varied on two levels. The levels of factors are shown in Table 3. Table 3 Levels of factors Levels Factors -1 0 +1 Spindle speed-n [rev/min] 320 405 560 Feed rate-Vf [mm/min] 62 93 175 Depth of cut-ap [mm] 0.4 0.7 1.2  The experimental research was carried out on the “Prvomajska” UGH universal milling machine, under the laboratory conditions. The force and moment were measured with a Kistler piezoelectric dynamometer, type 9123C. The experimental setup is shown in Fig. 2.  Fig. 2 Universal milling machine “Prvomajska” UGH Surface roughness was measured on a Mahr profilometer under the laboratory conditions, Fig. 3.  Influence of Cutting Parameters on Force, Moment and Surface Roughness in End Milling 5   Fig. 3 Mahr profilometer for measuring surface roughness The plan of the experiment and measurement results of force Fc, moment M and surface roughness Ra is shown in Table 4. Table 4 The plan of the experiment and measurement results No. n [rev/min] Vf[mm/min] ap[mm] n [rev/min] Vf [mm/min] ap[mm] Fc[N] M [Nm] Ra [μm] 1 -1 -1 -1 320 62 0.4 37.3 0.30 2.907 2 -1 -1 1 320 175 1.2 125.0 0.9 1.600 3 -1 1 -1 320 62 0.4 98.6 0.76 5.191 4 -1 1 1 320 175 1.2 211.8 2.42 4.267 5 1 -1 -1 560 62 0.4 31.6 0.26 1.673 6 1 -1 1 560 175 1.2 76.7 0.69 1.757 7 1 1 -1 560 62 0.4 74.6 0.57 3.348 8 1 1 1 560 175 1.2 174.9 1.45 3.301 9 0 0 0 405 93 0.7 55.0 0.55 1.945 10 0 0 0 405 93 0.7 50.0 0.50 1.976 11 0 0 0 405 93 0.7 60.0 0.58 1.988 3. ANALYSIS OF RESULTS AND DISCUSSION The cutting force, moment and surface roughness measurement results were analyzed by using the analysis of variance (ANOVA) in the Minitab 17 software package. It is clear from the results of ANOVA that depth of cut (ap) and feed rate (Vf) are the dominant factors affecting the cutting force. The factors influencing the force are: spindle speed (n), feed rate (Vf), followed by spindle speed (n), while the interaction between feed rate and depth of cut (Vfap) and that between spindle speed and depth of cut (nap) are also significant. The interaction between spindle speed and feed rate (nVf) and three ways interaction (nVfap) is not significant based on the P-value because its value is greater than 0.1 [12, 13, 14]. F-value is used to determine whether group means are equal, it is just a matter of including the correct variances in the ratio. The analysis of variance for the cutting force is given in Table 5.  6 J. STANOJKOVIĆ, M. RADOVANOVIĆ Table 5 Analysis of variance for cutting force Factors and interactions Sum of square Mean square F-value P-value N 1650.3 1650.3 66.01 0.015 Vf 10461.8 10461.8 418.47 0.002 ap 14990.5 14990.5 599.62 0.002 nVf 6.0 6.0 0.24 0.674 nap 385.0 385.0 15.40 0.059 Vfap 814.1 841.1 32.56 0.029 nVfap 110.3 110.3 4.41 0.171  All factors and interactions have a significant effect on the moment. The analysis of variance for the moment is given in Table 6.  Table 6 Analysis of variance for moment Factors and interactions Sum of square Mean square F-value P-value N 0.24851 0.24851 152.15 0.007 Vf 1.16281 1.16281 711.93 0.001 ap 1.59311 1.59311 975.37 0.001 nVf 0.10351 0.10351 63.38 0.015 nap 0.11281 0.11281 69.07 0.014 Vfap 0.28501 0.28501 174.50 0.006 nVfap 0.04651 0.04651 28.48 0.033 All factors and interactions have a significant effect on surface roughness. The analysis of variance for surface roughness is given in Table 7.  Factors and interactions Sum of square Mean square F-value P-value N 1.8876 1.88762 3834.04 0.000 Vf 8.3436 8.34561 16947.08 0.000 ap 0.6017 0.60170 1222.15 0.001 nVf 0.3750 0.37498 761.63 0.001 nap 0.6430 0.64298 1305.98 0.001 Vfap 0.0079 0.0794 16.12 0.057 nVfap 0.0330 0.03302 67.08 0.015  Based on the obtained data, the influence of the factors on the cutting force, moment and surface roughness in the end milling of aluminum 6082-T6 can be determined. The greatest effect on the cutting force and moment during the end milling of aluminum 6082-T6 with solid carbide end mill has the depth of cut, followed by the feed rate and the spindle speed. By increasing the depth of cut and the feed rate, the cutting force and the moment increase, while increasing the spindle speed causes decrease of the cutting force and moment, Fig. 4 (a), (b). The effect on surface roughness during the end milling of aluminum 6082-T6 has the feed rate. By increasing the feed rate, surface roughness increases, while increasing the spindle speed and depth of cut causes decrease of surface roughness, Fig. 4 (c).  Influence of Cutting Parameters on Force, Moment and Surface Roughness in End Milling 7    (a)  (b)  (c) Fig. 4 Influence of n, Vf and ap on: a) cutting force, b) moment and c) surface roughness To simulate the process in terms of the cutting force, a mathematical model was developed using the multiple regression method. The mathematical model is given in Eq. (1):  ppfpfc naaVaVnF 94.609.1029.4316.3636.1481.103 −+++−=  (1) The coefficient of determination is R2=99.85%, while the adjusted coefficient of determination is R2(adj)=99.26%.  The mathematical model of the moment is given in Eq. (2): pfpfpfpf anVaVnanVaVnM 0763.01888.01187.01137.04462.03812.01763.09188.0 −++−−++−=  (2) 8 J. STANOJKOVIĆ, M. RADOVANOVIĆ The coefficient of determination for the moment is R2=99.92%, while the adjusted coefficient of determination is R2(adj)=99.58%. The mathematical model of surface roughness is given by Eq. (3): pfpfpfpf anVaVnanVaVnRa 06425.00315.02835.02165.027425.002125.148575.00055.3 −++−−+−=  (3) The coefficient of determination of surface roughness is R2=99.99%, while the adjusted coefficient of determination is R2(adj)=99.97%. Based on the 3D surface plots of the cutting force, moment and surface roughness one can study the relations among the influencing factors during the end milling of aluminum alloy 6082-T6, Fig. 5.  (a)  (b)  (c) Fig. 5 3D surface plots of a) cutting force, b) moment and c) surface roughness 4. CONCLUSIONS Investigating the cutting force, moment and surface roughness is important for the process of milling. The cutting force and moment are the basic criteria for evaluation of machinability, while surface roughness is the basic criteria for the quality of parts. The knowledge of these performances facilitates the effective planning of the machining process. The measurement of the cutting force, moment and surface roughness was carried out for different values of spindle speed (320.405 and 560 rev/min), feed rate (62, 93 and 175 mm/min) and depth of cut (0.4, 0.7 and 1.2 mm) in the laboratory conditions on a  Influence of Cutting Parameters on Force, Moment and Surface Roughness in End Milling 9  universal milling machine during the milling of aluminum alloy 6082-T6 with solid carbide end mill, manufactured by Seco, without cooling. The cutting force and moment were measured using a Kistler piezoelectric dynamometer, while surface roughness was measured on a Mahr profilometer. Based on the experimental results of the cutting force, moment and surface roughness, an analysis was performed in the Minitab 17 software package. In the end milling of aluminum 6082-T6, the greatest impact on the cutting force and moment is achieved by the depth of cut, followed by the feed rate and the spindle speed. By increasing the cutting depth and the feed rate the main cutting force and moment grow as well, while increasing the spindle speed reduces them. On the other hand, the feed rate has the greatest influence on surface roughness. By increasing the feed rate, surface roughness increases as well, while increasing the speed and depth of cut causes decrease of surface roughness, i.e. a better quality of processing is achieved. Acknowledgements: The paper is a part of the research done within the project TR35034. The authors would like to thank to the Ministry of Education and Science, Republic of Serbia REFERENCES  1. Kovač, P., Savković, B., Mijić, A., Sekulić, M., 2011, Analytical and experimental study of cutting force components in face milling, Journal of Production Engineering, 3(1), pp. 15-18. 2. 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INFLUENCE OF THE CUTTING PARAMETERS ON FORCE, MOMENT AND SURFACE ROUGHNESS IN THE END MILLING OF ALUMINUM 6082-T6

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INFLUENCE OF THE CUTTING PARAMETERS ON FORCE, MOMENT AND SURFACE ROUGHNESS IN THE END MILLING OF ALUMINUM 6082-T6

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