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1 EFFECT OF MINIMUM QUANTITY LUBRICATION (MQL) ON CUTTING FORCES AND SURFACE ROUGHNESS IN TURNING OF EN16 STEEL USING VEGETABLE OIL Nirmal Kumar Lamba 1, Balvinder Budania 2, Jeewan Singh 3 1 M.Tech. Student, 2 Assistant Professor, Deptt. of Mechanical Engineering, OITM, Hisar, Haryana (INDIA) 3 Assistant Professor, Department of Mechanical Engineering, Chandigarh Group of Colleges, Landran, Punjab(INDIA) Abstract-Considerable attention has been given to reduce or completely omit the cutting fluids, and meet the demands for environment-friendly cutting processes. Turning with vegetable oil based Minimal quantity lubrication (MQL) is one such technique, which can alleviate the pollution problems associated with cutting fluids. The present work deals with experimental investigation in the role of MQL with sunflower vegetable oil (MQLSF) on cutting forces, temperature, surface finish and dimensional deviation in turning of EN-16 steel at industrial cutting speeds (25 and 70m/min) and feed (0.8 and 0.16mm/rev) combination by High speed steel tools. The results have been compared with dry machining and machining with soluble oil as coolant in flood machining. The results of the present work indicate substantial benefit of MQLSF on cutting forces, surface finish and dimensional deviation. This may be attributed mainly to the reduction in cutting zone temperature. Further it was evident that machining with soluble oil cooling failed to provide any significant improvement in tool life, rather surface finish deteriorated. The results indicate that there is a considerable improvement in the process performance with MQLSF assisted machining as compared to that of machining with dry and flood conditions. KeyWords:- Machining, Cutting Fluids, MQL, Cutting Forces I. INTRODUCTION THE growing demands for high productivity of machining require high material removal rates (MRR), which require high cutting speed and feed rate, but increase in MRR can lead to the shortening of tool life due to increase in friction and heat generation at the tool cutting zone (Trent and Wright, 2000). In machining, most of the mechanical energy associated with chip formation is converted into heat, thereby increasing temperature considerably. This temperature rise is known to cause thermal damage to both the tool and workpiece, such as rapid tool wear and dimensional errors (Sato et al., 2013). To reduce the cutting temperature and cutting forces, the cutting zone must be well lubricated and adequately cooled by applying coolants in most machining applications (Park et al., 2010). The main cause of energy loss in a mechanical system is the friction but this can be reduced by lubrication. Thus, it is very important to improve the lubrication properties. At dry cutting condition, high temperature is generated at the tool workpiece material interface. At high temperature, the nimmakarandi@gmail.com cutting tool become weak due to a high diffusion rate of carbide tool material into the workpiece material, leading to the accelerated of the tool wear and terminating the tool life (Ozcelik et al., 2011). Application of cutting fluids changes the performance of machining operations because of their lubrication, cooling and chip flushing functions (Dhar et al., 2007). Metal cutting fluids (MCFs) can change the potential of machining operations because of their lubrication, cooling and chip removal functions (Meena and Mansori, 2011). But the conventional cutting fluids/ MCFs are not that effective in such high production machining, particularly in continuous cutting of materials likes steels. However, the use of cutting fluids has caused some problems such as high cost, pollution, and hazards to operator s health. When inappropriately handled, cutting fluids may damage soil and water resources, causing serious loss to the environment. Therefore, the handling and disposal of cutting fluids must obey rigid rules of environmental protection (Dhar et al., 2007). Emulsionbased cooling fluids/mcfs for machining are still widely used in large quantities in industrial metal-mechanical processes, generating high consumption and disposal costs and harming the environment (Silva, 2007). All the problems related to the use of cutting fluids have urged researchers to search for some alternatives to minimize or even avoid the use of cutting fluids in machining operations. So far various alternatives have been offered. Some of these alternatives are minimal quantity lubrication {MQL} (Su et al., 2007). MQL refers to the use of cutting fluids of only a small amount, flow rate in the range of ml/h (Dhar et al., 2006). In MQL, a very small lubricant flow (ml/h instead of l/min) is used (Attanasio et al., 2006). In other words MQL is a technique that uses a spray of small oil droplets in a compressed air jet. The lubricant is sprayed directly into the cutting zone, avoiding the huge flows of conventional flood coolant methods (Oliveira et al., 2012). The MQL provide extra oxygen to chip-tool interface so as to promote the formation of a protective oxide layer. MQL is now of great interest and actually, they meet with success in the field of environmentally friendly manufacturing (Byrne and Scholta, 1993) The MQL is a recent technique introduced in machining (in particular, in turning) to obtain safe, environmental and economic benefits, reducing the use of coolant lubricant fluids in metal cutting. But a cutting fluid for MQL should be ISSN Page 22

2 selected not only on the basis of primary characteristics i.e. cutting performance but also of its secondary characteristics, such as biodegradability, oxidation stability and storage stability. However, there has been little investigation of the cutting fluids to be used in MQL machining. Stabler et al. (2003) suggested the types of fluids not applicable for the MQL were water mixed cooling lubricants and their concentrates. Krahenbuhl (2002), considered vegetable oils as viable alternative to petroleum-based metal working cutting fluids. Vegetable oils are renewable resources, environmentally friendly nontoxic fluids, pose no work place health hazards and are readily biodegradable (Salunkhe et al., 1992). The triacylglycerol structure of vegetable oil makes it an excellent candidate for potential use as a base stock for lubricants and functional fluids (Willing et al., 2001).In this context, cutting fluids based on vegetable oils and esters qualify as potential candidates to replace mineral-based products, because they are almost entirely biodegradable and well compatible with minimal lubrication technology (Belluco and Chiffre, 2004). Literature review shows the lack of study on the effects of MQL parameters such as oil flow rate, air pressure, MQL nozzle position and nozzle distance from the wheel workpiece contact zone. In this paper, experiments are conducted under different coolinglubricant conditions to determine the performance of the Table 1 Chemical composition of EN16 carbon steel MQL parameters, regarding turning forces and surface roughness. II. EXPERIMENTATION The work material used for the turning tests was EN16 steel, The chemical composition of the workpiece is given in Table mm diameter and 330 mm length workpieces were machined throughout the investigation. The experiments were performed on a powerful and self centring rigid lathe. High speed steel (HSS) cutting tools were used with the following tool geometry: Back rake angle-12, side rake angle-8, clearance angle-13, cutting edge angle-45 and nose radius mm depth of cut was kept constant during the turning tests. The experiments were performed under different conditions i.e. dry, flood and MQLSF (Minimum Quantity Lubrication with Sunflower oil). The measurement of cutting forces were carried out by using strain-gauge type three components lathe tool dynamometer An infrared thermometer (noncontact type) was used for the measurement of the toolwork-chip interface temperature, which is having the range of temperature measure from -100 to 700 C. Talysurf (Mitutoyo SJ-201) profilometer was used to measure the surface roughness on machined components. An average of four measurements was used as a response value (Ra). The Experimental input parameters are given in Table 2. Elements C Si Mn P S Cr Mo Ni Al Co Cu V Fe Nominal % max max Bal. Actual % Bal. Table 2 Machining parameters Cutting velocity (m/min) 25 and 70 Feed rate (mm/revolution) 0.08 and 0.16 Cutting length (mm) 175 Cutting oil and flow of MQL (ml/hr) Sunflower oil, 150 Cutting oil and oil supply for flood condition (lit/min) koolkut 40 (Hindustan Petroleum), 4 Compressed Air Pressure for MQL (bar) 6 Machining conditions Dry, flood, MQLSF Concentration of oil with water for flood condition 1:10 Nozzle distance from rake surface 15 mm ISSN Page 23

3 III. RESULT AND DISCUSSION A. CUTTING FORCES:- Fig 1 Cutting force, thrust force and feed forces during dry, flood, MQL machining conditions at cutting speed 25 m/min and feed 0.08 mm/rev. In Fig. 1, the effect of different cutting conditions (dry, flooded and MQLSF) is shown on cutting force at cutting speed of 25 m/min and feed rate of 0.08 mm/ rev. it is found that lowest cutting force, thrust force and feed force is obtained in MQLSF condition. The highest value of machining forces is observed in dry machining followed by flood machining. It can be concluded that at the low cutting speeds and feed rates, the access of the oil droplets to the cutting area is easier, therefore the lubricating effect of the MQL allows for reduction in the resultant forces. ISSN Page 24

4 Fig 2 Cutting force, thrust force and feed forces during dry, flood, MQL machining conditions at cutting speed 25 m/min and feed 0.16 mm/rev In Fig 2, as the feed rate increased from 0.08 to 0.16 mm/rev, the mean resultant forces are also increased. Cutting force in dry machining is higher than flood machining in every machining parameter. Feed rate greatly influence on the feed forces, those are rapidly increased in all machining conditions and also affect the thrust force. Due to increase in feed rate, thrust force is also increased which affect the tool life in great extent. But in MQLSF it is very low as compared to other machining conditions. This can be attributed to less chance of built up edge formation under high-pressure coolant environment is evident as a very small fluctuation of force is observed.reduction in chip-tool contact length and reduction in curl radius of the chips in MQLSF condition might have contributed in reducing the cutting forces. Fig 3 Cutting force, thrust force and feed forces during dry, flood, MQL machining conditions at cutting speed 70 m/min and feed 0.08 mm/rev. In Fig 3, as the cutting speed increased from 25 m/min to 70 m/min, there is slightly increase in all forces but MQLSF again proved its efficiency at higher speed. The magnitudes of cutting forces in MQLSF cutting condition are much smaller than that under dry cutting condition. The reduction of cutting forces indicates that the MQLSF technique has been successful in reducing the cutting force components at higher speed also. This is mainly attributed to the reduction of friction accomplished by the lubrication effect of the micro-droplets of the biodegradable vegetable oil. The microdroplets of the cutting oil with high pressure and high velocity are able to reach the cutting zone where it performed its lubrication effect and minimized the friction to a remarkable amount at reported by Zhang al al., On the other hand, the cooling effect of the compressed air could reduce the adhesion of the workpiece material on the tool faces. ISSN Page 25

5 Fig 4 Cutting force, thrust force and feed forces during dry, flood, MQL machining conditions at cutting speed 70 m/min and feed 0.16 mm/rev. As shown in Fig. 4, with the feed increased from 0.08 mm/rev to 0.16 mm/rev at 70 m/min cutting speed, higher feed forces are obtained when compared to all other experiments. The feed rate has the highest influence on the resultant force increase, which is mostly in accordance with an increase in the un-deformed chip area as suggested by Leppert, The highest cutting force is obtained in again dry condition. MQLSF gives the lowest resultant forces at higher feed and cutting speed. It is clearly noted that as feed rate is increased, higher feed force is obtained which also affect the other cutting forces. Also the lower adhesion produces lower frictional force during MQL condition. In short, the application of MQLSF on the tool faces can minimize the cutting forces thus saving the energy. In other words, MQLSF cutting with biodegradable vegetable oil can effectively improve the machinability of EN 16 steel, such as extension of tool life and reduction of cutting forces. B. SURFACE ROUGHNESS It is well known that the surface roughness significantly affects the material strength when specimens are subjected to fatigue cycles (Silva et al., 2007). Fig. 5 shows the surface roughness values recorded under dry, flood and MQLSF under different machining parameters. ISSN Page 26

6 Fig 5 Average surface roughness values at various cutting speeds and feed rate under different cutting conditions. The measured surface roughness is between 2.99 µm to 5.15 µm at 25 mm/min cutting speed and 0.08 mm/rev feed rate under the compared cutting conditions. As the feed rate increases from 0.08 to 0.16 mm/rev and cutting speed remains constant, the surface roughness also increased under all cutting conditions. Meanwhile, MQLSF recorded the surface roughness value between 2.45 to 3.24 µm for the aforementioned feed rates and cutting speed which is lowest as compared to dry and flood conditions. It can be observed from the figure that the surface roughness decreases with increase in cutting speed. The use of a higher cutting speed 70m/min, will therefore reduce the contact length of the tool-chip interface, thus reducing the cutting force. An increase in the cutting speed should lead to a decrease in the built-up edge, minimize the bending vibration of the tool and shaft, and decrease the irregular shape of the machined surface (El-Khabeery et al., 1991). A reduction in cutting force leads to the formation of less surface roughness. In addition, as the cutting speed increases, more heat is generated thus softening the workpiece material, which in turn improves the surface roughness. However, a low cutting speed may lead to the formation of a built-up edge and hence deteriorate the machined surface. Further as expected, increasing the feed rate results in increasing the surface roughness. The results revealed that the higher value of surface roughness is obtained at the higher value of feed rate (0.16mm/rev) and the lower value of cutting speed (25m/min). Further analysis revealed that the surface roughness was lower under the MQLSF condition for given cutting speeds and feed rates. When applying sunflower cutting oil (MQLSF) as the lubricant, more effective lubrication and cooling at the tool-work interface especially with a high cutting temperature, are generated, thus allowing the chips to flow away from the cutting zone due to higher pressure of air in MQL condition. As a result, the friction and temperature are reduced and surface roughness is lessened. So, results shows that MQLSF can be alternative for flood and dry cutting conditions and gives a improved surface roughness during turning of EN 16 steel. C. CUTTING TEMPERATURE Fig 6 gives the variation of cutting temperatures under different cooling-lubrication conditions. It can be seen that cutting temperature under different cooling conditions is increasing with the increasing of the cutting speed and feed rate. Fig 6 Average temperature values at various cutting speeds and feed rate under different cutting conditions. Highest cutting temperature 110 C is observed in dry machining at higher speed and feed rate. At higher speed and feed rate, more heat is generated due to high material removal rate. Due to this, there is increase in tool-chip interface temperature and thus increases in tool wear. These results reveals that the change in cutting speed and feed rate have a significant effect on the workpiece temperature.. But most important of all, there has been a substantial reduction in cutting temperature for MQLSF as compared with the other two cooling methods i.e. dry and flood, especially at higher cutting speed. It may also be concluded from the experimental results that there is only a slight increase in work piece temperature between flood and MQL lubrication, but MQLSF lubrication being superior at both the lower and higher machining parameters The cutting temperature with MQLSF at cutting speed of 70 m/min is below 62 C which is lower than those with dry and flood cooling. Flood cooling method mainly depends on the convection of the soluble oil in the cutting zone. The coolant will boil and vaporize under high temperature above in the cutting zone. It will result in a vapour film ISSN Page 27

7 layer, which may prevent the penetration of the coolant into chip tool interface or the cutting zone and influence the cooling effect of the coolant. With the rising of cutting temperature, the cooling effect for the flood cooling method will become worse. A good penetration for MQLSF can be obtained with the impingement effect of high velocity droplets, which can enter into chip tool interface and reduce the contact length between the chip and rake face of the cutting tool by lifting of the chip. The minute droplets of lubricating oil, which is helpful for improvement of lubrication at the chip tool interface. The cooling capability of MQLSF is effectively enhanced during the turning process because the heat transfer effect of vaporization is greater than that of convection. Therefore cutting temperature with MQLSF can be reduced efficiently. IV. Conclusions Experiments are conducted to investigate the mechanism of MQLSF in turning of EN16 steel. It is found that comparing with dry and flood machining; the machining performance of MQLSF can be enhanced under all cutting speeds in this study. The following can be concluded: o The MQLSF lubrication-cooling technique does significantly affect the cutting forces and produces the lowest cutting forces at all cutting speeds and feed rates. o Wet cutting produces the highest surface roughness But Surface finish improved under pure MQL condition compared to machining with flood and dry cutting conditions. Chip morphology was also acceptable in MQLSF condition. o Cutting temperature can be reduced more effectively with MQLSF than that with dry and flood cooling methods, especially at higher cutting speed. Due to its better cooling and lubrication effects, tool life was improved effectively. o MQL with vegetable oil would be a good eco-friendly cooling-lubrication method that is suitable for turning process of medium carbon steels and rust problem of the machine tool aroused by water soluble cutting oil is resolved. REFERENCES 1. A. Attanasio, M. Gelfi, C. Giardini and C. Remino, Minimal quantity lubrication in turning: effect on tool wear, Wear 260 (2006) A. Meena and M.E. Mansori, Study of dry and minimum quantity lubrication drilling of novel austempered ductile iron (ADI) for automotive applications, Wear 271 (2011) A. Willing, Lubricants based on renewable resources-an environmentally compatible alternative to mineral oil products, Chemosphere 43 (2001) B. Ozcelik, E. Kuram, M.H. Cetin and E. Demirbas, Experimental investigations of vegetable based cutting fluids with extreme pressure during turning of AISI 304L, Tribo International, 44 (12) (2011) D.de J. Oliveira, L.G. 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