Surface Quality Improvement in CNC End Milling of Aluminum Alloy Using Nanolubrication System Mohd Sayuti Ab Karim, Ahmed Aly Diaa Mohammed Sarhan and Mohd Hamdi Abd Shukor

Abstract Aerospace applications and energy saving strategies in general raised the interest and study in the field of lightweight materials, especially on aluminum alloys. Aluminum Al2017-T4 and Al6061-T6 alloy which are used in this research work have low specific weight and high strength.The (CNC) milling machine facilities provides a wide variety of parameters setup, making the machining process of the aluminum alloy excellent in manufacturing complicated special products. However, the demand for high quality focuses attention especially on the roughness of the machined surface. The key solution for this issue is by introducing the nanolubrication system since it could produce much less friction in the tool-chip interface. In this research work, the Al2017-T4 and Al6061-T6 is machined by using the carbon onion nanoparticle and SiO2 nanoparticles, respecticely when it mixed with ordinary mineral oil at various concentrations as a nanolubrication system. The reduction of surface roughness could be obtained when carbon onion and SiO2 nanolubricant are used compared with the case of using ordinary lubricant due to the tribological properties of the carbon onion and SiO2 nanolubricant to reduce the coefficient of friction in the tool-chip interface. Keywords Al2017-T4 alloy · Al6061-T6 alloy · Carbon onion nanolubrication End milling · Morphological surface · SiO2 nanolubrication · Surface quality

·

M. S. A. Karim (B) · A. A. D. Mohammed Sarhan · M. H. A. Shukor Centre of Advanced Manufacturing and Material Processing, Department of Engineering Design and Manufacturing, Engineering Faculty, University of Malaya, 50603 Kuala Lumpur, Malaysia e-mail: [email protected] A. A. D. Mohammed Sarhan e-mail: [email protected] M. H. A. Shukor e-mail: [email protected] G.-C. Yang et al. (eds.), IAENG Transactions on Engineering Technologies, Lecture Notes in Electrical Engineering 229, DOI: 10.1007/978-94-007-6190-2_51, © Springer Science+Business Media Dordrecht 2013

669

670

M. S. A. Karim et al.

1 Introduction Aluminum and its alloys are today considered one of the most practical of metals for a variety of reasons. Its low cost, light-weight, and modern appearance are among the primary reasons for its widespread use. Furthermore, it is non-sparking, electrically conductive, thermally conductive, non-magnetic, reflective, and chemically resistant. Aluminum Al2017-T4 and Al6161-T6 are among of the highest strength and hardest aluminium alloys with excellent fatigue strength available. Heat-treating increases its strength considerably. It is used for various applications from high strength structural components, aircraft, machine construction, military equipment, rivets. Aluminum Al2017 and Al6061-T6 also has very good machining characteristics and it is best to perform machining with the alloy in the T4 and T6 condition [1]. After the machining process, the existence of clean surfaces and high hydrostatic stresses favors the formation of strong adhesive friction junctions; the extent of these can be limited by the provision of a suitable lubricant [2–4]. Correct application of lubricants has been proven to greatly reduce friction. This results in surface quality improvement [5]. Although the significance of lubrication in machining is widely recognized, the usage of conventional flooding application in machining processes has become a huge liability. Not only does the Environmental Protection Agency regulate the disposal of such mixtures, but many countries and localities also have classified them as hazardous wastes. Beside that economically, the cost related to the lubrication and cutting fluid is 17 % of total production cost which is normally higher than that of cutting tool equipments which incurs only 7.5 % of total cost. At present, many efforts are being undertaken to develop advanced machining processes using less lubrications [6]. Promising alternatives to conventional flood coolant applications are the minimum quantity lubrication (known as MQL) [7]. Klocke and Eisennblatter (1997) state that MQL refers to the use of lubrication of only a minute amounttypically of a flow rate of 50–500 ml/h which is about three to four orders of magnitude lower than the amount commonly used in flood cooling condition. This has been reported to improve tool life due to its ability to penetrate into the tool-chip interface, this results in improving surface quality [8]. For more develop advanced machining processes for better surface quality using less lubrication, it is clear that a multi-pronged approach must be used, including innovation in technology [9]. In this chapter, authors will explore the development of nanolubrication in machining. It has been reported that, by introducing the nanolubrication system in machining process, the reduction of friction component could be achieved as it is working of billions of rolling elements in the tool-chip interface and consequently produce much better surface quality [10]. Nanolubricant is defined as new engineering material consisting of nanomaterial sized particles dispersed in base fluid. The nanolubricant is developed to sustain the high machining temperatures present in machining process, non-toxic, easy to be applied and effective in term of cost [11]. Over a decade, carbon onion has been successfully developed with high tribology performance. It consist of concentric graphitic shells and it is

Surface Quality Improvement in CNC End Milling of Aluminum Alloy Using NS

671

one of the fullerene-related materials together with C60 and carbon nanotubes [12]. It has been proved that it can provide the similar lubrication with the graphite when tribologically tested at ambient air. It is expected to have good properties suitable for nanobrication system due to its unique structure. It also has been proved that it could be used as a solid additive to grease replacing MoS2 in several commercially available lubricants for use in ambient air [13]. On the other hand, silicon dioxide (SiO2 ) nanoparticle is a hard and brittle material. This nanoparticle has very good mechanical properties especially in term of hardness (Vickers hardness—1,000 kgf mm−2 ) and in very small size range from 5 nm up to 100 nm. Following the review above, in this research work, the surface quality improvement is investigated in end milling of Al2017-T4 alloy using carbon onion nanolubrication. Also, the surface quality and surface morphology of Al6061 material was investigated when using SiO2 nanoparticles at different concentration in milling process.

2 Experimental Set Up and Procedure The experimental set-up used in this study is illustrated in Fig. 1. The machine used in this study is a vertical type machining centre (Sakai CNC MM-250 S3), in which the spindle has constant position preloaded bearings with oil-air lubrication and the maximum rotational speed is 5,000 min−1 . The tool used in the experiments is SEC-ALHEM2S8 end mill having a diameter of 8 mm, as shown in Fig. 2. The cutting processes of rectangular Al2017-T4 and Al6061-T6 workpiece (118 HV) with dimension of 50 × 20 × 10 mm3 are selected as the case study. Table 1 shows the mechanical properties of Al2017-T4 and Al6061-T6, and Fig. 3 shows the workpiece and tool path in the cutting tests. The slot-milling test is carried out and the tool moves in the + X direction to cut a stroke of 50 mm. The cutting speed, feed rates and depths of cut are set at 75.408 m/min, 100 mm/min and 1.0 mm, respectively, and are selected based on the recommendations given by the tool manufacturer. Fig. 1 Experimental set-up

672

M. S. A. Karim et al.

Fig. 2 The tool geometry Table 1 The mechanical properties of Al2017 and Al6061

Mechanical properties

Al2017-T4

Al6061-T6

Hardness, Vickers Ultimate tensile strength (MPa) Tensile yields strength (MPa) Modulus elasticity (GPa) Poisson ratio Fatigue strength (MPa) Shear modulus (GPa) Shear strength (MPa)

118 427 276 72.4 0.33 124 27 262

107 310 276 68.9 0.33 96.5 26 207

Fig. 3 Workpiece and tool path

In case of using carbon onion nanoparticle, the Alumicut lubricant type is chosen to reduce friction at the tool-chip interface due to its favorable lubrication characteristics. There are four different lubrication modes used in this study which consist of 0.0, 0.5, 1.0 and 1.5 %wt of carbon onion mixed with Alumicut oil, followed by sonification using Sono Bright ultrasonic vibration (240 V, 40 kHz, 500 W) for 30 min in order to suspend the particles homogeneously in the mixture. In case of using more than 1.5 %wt concentration, the mixing process of carbon onion in oil is challenging as the onion particles tend to collect together, having high weight and finally agglomerate. In future, more investigation is needed to solve this mixing problem.

Surface Quality Improvement in CNC End Milling of Aluminum Alloy Using NS

673

Fig. 4 TEM picture of carbon onion [7]

Fundamentally, carbon onion nanoparticles are produced by heat-treatment of carbon black (Cabot R250 from Cabot Corporation) in a resistance-heated furnace using a graphite crucible under Helium gas at a pressure of 1 atm. The nano-size carbon onion is obtained by inductive heating at 2000 ◦ C for 15 min and is used without further treatment (i.e. purification). Figure 4 shows the TEM image of carbon onion with an average size of 5–20 nm. In the mean time, for SiO2 nanolubrication, four different concentration of 0, 0.2, 0.5 and 1.0 wt% were used in order to investigate its effect to the morphological surface. The nanolubricant were prepared by mixing SiO2 nanoparticles with an average size of 5–20 nm to the mineral oil followed by sonification (240 W, 40 kHz, 500 W) using Sono Bright ultrasonic device for 5 h in order to suspend the particle homogeneously in the mixture. To ensure the consistent lubrication supply into the systems for both cases of nanolubricant, the experimentation is carried out using MQL with a thin-pulsed jet nozzle that is developed in laboratory and controlled by a variable speed control drive. The diameter of the nozzle orifices is 1 mm and the nozzle system is attached to a flexible portable fixture fixed on the machining spindle without interfering with the tool or workpiece during the machining process. The surface roughness (Ra ) is measured using Nanofocus roughness tester equipped with µsufr Software under a magnification of 10×, in accordance to the ISO 11562 standard with a 0.6 mm cutoff distance. Surface roughness measurements are performed and repeated at three different spots for each measurement, one in the middle and the other two on the edge, were used to measure the surface roughness of the cut. Following this, the mean of the three readings is recorded. Furthermore, the Field Emission Scanning Electron Microscopy (FESEM) was utilized to examine the morphology of machined surface.

674

M. S. A. Karim et al.

3 Results 3.1 The surface Roughness Results 3.1.1 Surface Roughness Results Using Carbon Onion Nanolubricant In case of using carbon onion nanolubrication system, the slot-milling test is carried out to investigate the surface quality improvement of the machined Al2017-T4. Figure 5a–d show the measured surface roughness for different carbon onion concentrations. The average measured surface roughness Ra at different carbon onion concentrations plotted in Fig. 6. As can be seen in Fig. 6, the lowest surface roughness values are obtained at the highest carbon onion concentration. In addition, the surface roughness improvements percentages are found to be 46.32 % compared with the case of using ordinary lubrication system. These results are totally supported by Fig. 7a–d which showing the stereoscopic photographs for three-dimensional views

(a)

(b)

(c)

(d)

Fig. 5 Measured surface roughness (Ra ) at different carbon onion concentration a 0 %wt carbon onion concentration b 0.5 %wt carbon onion concentration c 1.0 %wt carbon onion concentration d 1.5 %wt carbon onion concentration

Surface Quality Improvement in CNC End Milling of Aluminum Alloy Using NS

675

Fig. 6 Average of measured surface roughness (Ra ) at different carbon onion concentration

(a)

(b)

(c)

(d)

Fig. 7 Stereoscopic photographs for three-dimensional views of machined surface at different concentration a 0 %wt carbon onion concentration b 0.5 %wt carbon onion concentration c 1.0 %wt carbon onion concentration d 1.5 %wt carbon onion concentration

of machined surface at different modes of carbon onion concentration. It is clearly shown that the lowest surface roughness is obtained at the highest carbon onion concentration, with a concentration of 1.5 %wt.

3.1.2 Surface Roughness Results Using SiO2 Nanolubricant The slot milling test was carried out to investigate machining performance by using the proposed experimental setup. Figure 8 illustrates the samples of measured surface roughness at 5, 000 min−1 cutting speed, 100mm/min feed and 5mm depth of cut,

676 Fig. 8 The measured surface roughness at 0.2 wt% SiO2 nanoparticle concentration

M. S. A. Karim et al. 2.40 [µm] 1.20 0.00 -1.20 -2.40 -3.60 0.0

140.0

280.0

420.0

560.0 [µm] 700.0

using 0.2 wt% SiO2 nanoparticle concentration. While Fig. 9 shows surface roughness variations at different SiO2 nanoparticle concentrations. As can be seen from Fig. 9, the best roughness were obtained at 1.0 wt% of SiO2 concentration in which 36.82 % better compared with the case of using ordinary lubrication system. The mechanism behind such phenomena could be elaborated as being due to the increment of SiO2 concentration, which increases the existence of nanoparticles at the tool-chip interface, and these nanoparticles serve as spacers, which eliminate the contact at tool-chip interface. In high speed machining processes, the high heat generated changes elastohydrodynamic lubrication to boundary lubrication. The spherical nanoparticles cause a rolling effect in between the rubbing surfaces, and reduce the coefficient of friction [14, 15]. The low friction behavior of nanoparticles effectively minimizes the frictional effects at the tool-chip interface and thus improves the machined surface. Moreover, when large amounts of nanoparticles exist in cutting oil, it would collide and impeded by the asperities on the work surface and hence generate a better machined surface. On the other hand, the extensively dispersed SiO2 nanoparticles in cutting oil are facilitated by a high pressure air stream at the cutting zone, showing good per-

Fig. 9 Average of measured surface roughness at different SiO2 concentration

Surface Quality Improvement in CNC End Milling of Aluminum Alloy Using NS

677

formance in improving the machined surface. The atomized mist mixed with SiO2 nanoparticles suspended lubrication exhibited more efficient feeding at the cutting zone compared with the flood lubrication method. The presence of nanoparticles at the tool-chip interface acts as a polisher, since an interacting force is induced at the interface and hence, improves the surface quality.

3.2 The Morphology of the Machined Surface For further investigation on machining performance using SiO2 nanolubrication, the Field Emission Scanning Electron Microscopy (FESEM) was utilized to examine the machined surface morphology. At the beginning, substrate cleaning was required to remove all unwanted surface contamination. Substrate surface finish was achieved by etching in hot solutions of sodium hydroxide to remove minor surface imperfections. To remove surface oxides, which are a combination of inter metallic, metal and metal oxides remaining on the surface after cleaning/etching, an aqueous solution containing an oxidizing inorganic acid, phosphoric and sulfuric acids, simple and complex fluoride ions, organic carboxylic acid, and manganese in its oxidation state was used. The formation and growth of the protective SiO2 thin film on the machined surface were examined through surface elemental mapping analysis.

3.2.1 The Formation and Growth of the Protective SiO2 Thin Film on the Machined Surface Figure 10 shows the FESEM image of machined surfaces produced at four different SiO2 concentrations of 0, 0.2, 0.5 and 1.0 wt%. Clearly, many protective thin films were produced on the feed marks of the machined surface containing billions of SiO2 nanoparticles which provide much less friction and thermal deformation, as shown in Fig. 10b–d. These regular thin film formations grew when the SiO2 concentration was increased from 0.2 to 1.0 %wt. It was also observed in the surface layer that small exfoliations or shedding of the thin film occurred, as is illustrated by Fig. 10d. This could be explained by the fact that the increment of nanoparticle concentration increases the viscosity of cutting oil. In this case, more nanoparticles exist between the tool-chip interface and these nanoparticles will serve as spacers which eliminate the tool-chip contact friction. Moreover, due to the porous nature of spherical SiO2 nanoparticles, it could impart high elasticity, which augments their resilience in a specific loading range and enhances the gap at the tool-chip interface [16]. Therefore, with the extreme pressure of additives in cutting oil and the existence of a gap at tool-chip interface, there is a high contact resistance which induces the formation of film on the workpiece surface through chemical reaction [17]. In addition, the generation of high heat in the cutting zone will change elastohydrodynamic lubrication to boundary lubrication. This results in the formation of thin protective films on the surfaces, as per Fig. 10. The increment of nanolubricant concentration

678

M. S. A. Karim et al.

(a) 0%wt SiO 2 concentration

(b) 0.2%wt SiO 2 concentration

(c)

(d)

Fig. 10 FESEM on sample (a), (b), (c) and (d) which machined with 0, 0.2, 0.5 and 1.0 wt% of SiO2 concentration respectively

increases the growth of thin protective film on machined surfaces due to the breaking process. In other words, during machining the high number of nanoparticles rubs with the asperities at the workpiece surface and, thus, the newly created surface is exposed to cutting oil more frequently. In this way, strong chemical interaction is formed between nanolubricant and newly created surface and, therefore, a more intensive protective film is formed. This process definitely increases the quality of the machined surface, successfully enhancing the surface properties and reducing its coefficient of friction [18, 19].

3.2.2 Surface Elemental Mapping Surface elemental mapping was employed to investigate the relation between the machined surface quality and the orientation and distribution of SiO2 nanoparticles on the machined surface. Elemental mapping of samples machined with 0.2, 0.5 and 1 wt% are shown in Fig. 11a–c, respectively. Figure 11a shows that at 0.2 wt% SiO2 nanoparticles, the polishing track orientation matched the SiO2 nanoparticle distribution on the machined surface, especially at the exfoliated thin film. By using 0.5 wt% SiO2 nanoparticles, higher amounts of SiO2 nanoparticles were present compared to the case of using 0.2 wt%, as shown in Fig. 11b. With 0.5 wt%

Surface Quality Improvement in CNC End Milling of Aluminum Alloy Using NS

679

(a)

(b)

(c) Fig. 11 Surface elemental mapping of sample machined with different SiO2 nanoparticle concentration a Machined surface using 0.2 wt% of SiO2 nanoparticle concentration b Machined surface using 0.5 wt% of SiO2 nanoparticle concentration c Machined surface using 1.0 wt% of SiO2 nanoparticle concentration

SiO2 nanoparticles the track of embedded nanoparticles on the machined surface was clearly seen. Eventually the nanoparticles could be ploughed off but left debris nanoparticles behind. When the SiO2 nanoparticle concentration was increased up to 1.0 wt% as illustrated in Fig. 11c, higher amounts of SiO2 nanoparticles were embedded on the machined surface compared to the cases of 0.2 and 0.5 wt%. It was

680

M. S. A. Karim et al.

clearly seen that the nanoparticles were burnished on the porous alumina. Several SiO2 nanoparticles were partially embedded into the surface and some showed the tracks from being ploughed off, and more nanoparticle debris was left on it. Following the results of elemental mapping shown in Fig. 11a–c, the mechanism of nanoparticles was found to assist the cutting operation and can be categorized into the three levels. At the first level, the particles were partially embedded on the machined surface when they collided with its asperities due to extremely high pressure in the cutting zone; the particles were sheared and changed shape because of compression. The sheared off debris continues to assist the cutting, but not as well as spherical nanoparticles which exercise rolling with a low coefficient of friction. At the second level, with a higher concentration of nanoparticles, the partially embedded particles were ploughed off by new nanoparticles, and both then continued to polish the surface. The ploughed off particles left a thin exfoliated film on the contact area due to the damage from high loading [20–22]. Meanwhile, when nanoparticle concentrations continued to increase, those nanoparticles were impregnated into the pore of the surface and were then sheared by other incoming nanoparticles. The rolling of nanoparticles leads to the formation of an easily sheared lubrication film as well as the asperities on the surface, thus the surface is being polished and enhanced in quality. Therefore, as shown in the results, the 1.0 wt% concentration provided the best machined surface morphology compared to other concentrations.

4 Discussion In this study, the carbon onion and SiO2 are used as solid nanoparticle and mixed with ordinary mineral oil at different concentrations in order to investigate the surface quality improvement in CNC end milling machined of Al2017-T4 and Al6061-T6, respectively. For both cases, it is clearly seen that highest carbon onion and SiO2 concentration are producing the best surface quality. This could be explained as depicted in Fig. 12 with the fact that the deformation of the chip is flowing over the tool leads to localized regions of intense shear occurring due to the friction at the rake face, which is known as secondary shear. At higher plastic deformation chip is welded to the tool face and hence effectively changes tool geometry and rake steepness. This results in poor surface finish since the bits of the welded chip will eventually break off and stick to the workpiece. These bits tend to be problematic due to the work-hardening which they underwent very hard and abrasive. Applying the lubrication system to the tool-chip interface will reduce the coefficient of friction leading to better surface quality. However, introducing of the carbon onion and SiO2 nanolubrication system would show much less friction and much better surface quality. This is mainly attributed to the tribological properties of the nanoparticle which reduces the coefficient of friction at the interface during the machining as it is acting as billions of nano-scale quasi-spherical structure rolling elements, as shown in Fig. 13.

Surface Quality Improvement in CNC End Milling of Aluminum Alloy Using NS

681

Fig. 12 Shear mechanism in cutting zone [23]

Fig. 13 Rolling element in the tool-chip interface [24]

5 Conclusion In this study, the surface quality improvement of CNC end milling machined Al2017T4 and Al 6061-T6 using carbon onion and SiO2 nanolubrication system has been investigated, respectively. Based on the results obtained, the highest concentration of carbon onion and SiO2 nanoparticles produces the best surface quality. In addition, surface roughness reduction percentage in case of using carbon onion and SiO2 nanoparticle are found to be 46.32 and 36.82 %, respectively, compared with those obtained when using ordinary lubrication oil. The results are mainly attributed to the tribological properties of the carbon onion and SiO2 solid nanoparticle, which act as billions of nano-scale spherical structure rolling elements at the tool-chip interface. Consequently, the coefficient of friction at tool-chip interface is reduced significantly. With such excellent properties of carbon onion and SiO2 nanoparticles, it might be a new effective way as an alternative to flood lubrication due to the environmental issues involved. Acknowledgments The authors would like to acknowledge the University of Malaya, Malaysia and Tokyo Institute of Technology, Japan for providing the necessary facilities and resources for

682

M. S. A. Karim et al.

this research. This study was partially funded by HIR Grant no. HIR-MOHE-D000001-16001. The authors gratefully acknowledge the Ministry of Higher Education Malaysia for the financial support.

References 1. Sayuti M, Tanaka T, Sarhan AAD, Saito Y, Hamdi M (2012) Surface quality improvement in CNC milling machined aerospace AL-2017-T4 alloy using carbon onion nanolubrication with DLC coated cutting tool. In: Lecture notes in engineering and computer science : proceeding of the world congress engineering 2012, WCE 2012, London, U.K., pp 1487–1491 2. Lathkar GS, Bas USK (2000) Clean metal cutting process using solid lubricants. In: Proceeding of the 19th AIMTDR conference. Narosa Publishing House, IIT Madras, pp 15–31 3. Suresh Kumar Reddy N, Venkateswara Rao P (2006) Enhancement of machinability of AISI1045 steel using molybdenum disulphide as a solid lubricant. In: 2006 ASME international mechanical engineering congress and exposition, IMECE2006. American Society of Mechanical Engineers, Chicago, IL, United States, 5–10 November 2006 4. Belgasim O, El-Axir MH (2010) Modeling of residual stresses induced in machining aluminum magnesium alloy (Al–3Mg). In: Proceedings of the world congress on engineering 2010, WCE 2010, London, U.K., June 30–July 2 2010 5. Spanoudakis P, Tsourveloudis N, Nikolos I (2008) Optimal selection of tools for rough machining of sculptured surfaces. In: Proceedings of the international multiConference of engineers and computer scientists 2008, IMECS 2008, Hong Kong, 19–21 March 2008 6. Dilbag S, Rao PV (2008) Performance improvement of hard turning with solid lubricants. Int J Adv Manuf Technol 38:529–535 7. Yassin IN, Hamdi M, Fadzil M, Norhirni MZ (2011) Investigation into new development of minimal quantity lubricant (MQL) system in high speed milling of H13. In: UK–Malaysia–Ireland engineering science conference 2011 (UMIES 2011): Faculty of Economics & Administration, University Malaya, Kuala Lumpur 8. Klocke F, Eisenblätter G (1997) Dry cutting. CIRP Ann Manuf Technol 46(2):519–526 9. Sarhan AAD, Hassan MA, Matsubara A, Hamdi M (2011) Compensation of machine tool spindle error motions in the radial direction for accurate monitoring of cutting forces utilizing sensitive displacement sensors. In: Proceedings of the world congress on engineering (2011) WCE 2011, London 10. Reddy NSK, Nouari M (2011) The influence of solid lubricant for improving tribological properties in turning process. Lubr Sci 23(2):49–59 11. Deshmukh SD, Basu SK (2006) Significance of solid lubricants in metal cutting. In: 22nd AIMTDR 12. Hirata A, Igarashi M, Kaito T (2004) Study on solid lubricant properties of carbon onions produced by heat treatment of diamond clusters or particles. Tribol Int 37:899–905 13. Street KW, Marchetti M, Wal RLV, Tomasek AJ (2004) Evaluation of the tribological behavior of nano-onions in Krytox 143AB. Tribol Lett 16:143–149 14. Ramana SV, Ramji K, Satyanarayana B (2010) Studies on the behaviour of the green particulate fluid lubricant in its nano regime when machining AISI 1040 steel. Proc Inst Mech Eng Part B J Eng Manuf 224(10):1491–1501 15. Shenoy BS, Binu KG, Pai R, Rao DS, Pai RS (2012) Effect of nanoparticles additives on the performance of an externally adjustable fluid film bearing. Tribol Int 45(1):38–42 16. Zhang B-S, Xu B-S, Xu Y, Gao F, Shi P-J, Wu Y-X (2011) CU nanoparticles effect on the tribological properties of hydrosilicate powders as lubricant additive for steel–steel contacts. Tribol Int 44(7–8):878–886 17. Lin YC, So H (2004) Limitations on use of ZDDP as an antiwear additive in boundary lubrication. Tribol Int 37:25–33

Surface Quality Improvement in CNC End Milling of Aluminum Alloy Using NS

683

18. Lee K, Hwang Y, Cheong S, Choi Y, Kwon L, Lee J, Kim SH (2009) Understanding the role of nanoparticles in nano-oil lubrication. Tribol Lett 35:127–131 19. Zalnezhad E, Sarhan AAD, Hamdi M (2013) Optimizing the PVD TiN thin film coating’s parameters on aerospace AL7075-T6 alloy for higher coating hardness and adhesion with better tribological properties of the coating surface. Int J Adv Manuf Technol 64(1–4):281–290 20. Kragelsky IV, Zolotar AI, Sheiwekhman AO (1985) Theory of material wear by solid particle impact—a review. Tribol Int 18(1):3–11 21. Raadnui S (2005) Wear particle analysis—utilization of quantitative computer image analysis: a review. Tribol Int 38(10):871–878 22. Williams JA (2005) Wear and wear particles—some fundamentals. Tribol Int 38(10):863–870 23. Trent EM, Wright PK (2000) Metal cutting, 4 edn. Butterworth-Heinemann, Boston 24. Yan J, Zhang Z, Kriyagawa T (2011) Effect of nano-particle lubrication in diamond turning of reaction-bonded SiC. Int J Autom Technol 5(3):307–312