POTENTIAL OF VEGETABLE OILS AS MICRO LUBRICATION / COOLING MEDIUM FOR SQL- GRINDING

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1 POTENTIAL OF VEGETABLE OILS AS MICRO LUBRICATION / COOLING MEDIUM FOR SQL- GRINDING ManojKumar K 1, Jeewan Sarda 2, Amitava Ghosh 3 * 1 Dept. of Mech. Engg., IIT Madras, manojkannani2008@gmail.com 2 Dept of Mech. Engg., IIT Madras, jeewan.iitm@gmail.com 3* Dept. of Mech. Engg., IIT Madras, amitava_g@iitm.ac.in Abstract Scope and effectiveness of using vegetable oils as an environment friendly small quantity lubrication (SQL) medium have been investigated in the present work, where hardened AISI steel was ground by an alumina wheel in plunge mode. Palm oil and sunflower oil, which are two easily available vegetable oils in Indian market, were selected and characterized for wetting capability and lubricity. Sunflower oil was found to outperform its counter part and synthetic soluble oil in producing good wetting and effective lubrication on alumina and steel surface. Further grinding experiments were carried out to evaluate performance of the vegetable oils and the same was compared with that of conventional soluble oil. Performance was analysed in terms of grinding force, surface roughness and G-ratio. Sunflower oil was found to be the most effective to reduce grinding force and enhance G-ratio. Keywords:Metal working fluid (MWF), SQL grinding, Vegetable oils, G-ratio. 1 Introduction Metal working fluid (MWF) is essential for achieving adequate cooling and lubrication at the machining interface, especially in case of high specific energy involved processes like grinding. Additionally they are effective in removing chips from the machining zone, protecting the workpiece and tool surfaces from corrosion and reducing adhesion of the workpiece to the cutting tool. Grinding, being a high specific energy process, requires adequate volume of high quantity MWF to produce products with precise dimensions and defect free surface. Most of the commercial MWF s are mineral oil based fluids, which are applied in flood mode for effective heat dissipation and lubrication. The process includes the cost of recycling and waste disposal and often associated with environmental hazards and potential health risk to operators [W.J. Bartz1998]. The cost of recycling and disposal of MWF can be avoided by adopting minimum quantity lubrication (MQL) technology. In MQL, a small volume of metal working fluid (MWF) is broken into a large number of micro-droplets with the help of a suitably designed nozzle and highly pressurized air stream, thus increasing the total effective area of the heat dissipating medium. A number of investigations have already been carried out in the area of MQL in almost all machining operations, maintaining the flow rate between 5ml/hr and 100ml/hr [Silva et al. 2007, Tawakoli et al. 2009, Sadeghi et al. 2010]. Since grinding is a process associated with a large amount of specific energy a slightly high flow rate is always recommended [Shen Bin et al. 2008, Manoj Kumar et al. 2013]. A more general terminology SQL has been used in the place of MQL to represent wider range of cutting fluid flow rates varying from 1 to 1000 ml/hr. But use of synthetic soluble oil at high flow rates under SQL mode can create a huge amount of mist which in turn causes health problems to operators. So, in order to keep the sustainability effect in SQL grinding bio degradable oils are being used in the place of synthetic soluble oil. A number of researches have already been carried out in this area which inevitably showed the effectiveness of vegetable oil as coolant/ lubricant in different machining operations. Sharif et al. (2009) observed that end milling of AISI 4200 steel under MQL mode using palm oil as cutting fluid can produce a longer tool life and better finish. A similar trend of improvement in surface finish and increased productivity were achieved by Khan et al. (2009) during the turning of AISI 9310 alloy steel using food grade vegetable oil under MQL mode.alves and Oliveira (2006) developed a vegetable oil based cutting fluid and studied its performance during the grinding of SAE 1020 steel using CBN wheel. They were able to obtain a reduction in wheel wear and workpiece roughness at 21% concentration of the new cutting fluid. The effect of cutting fluid types and machining parameters on roughness and force during the drilling of AISI 3040 steel was studied by Kuram et al.(2010). Three different vegetable oils duly modified with various additives for reducing corrosion, bacterial growth, 387-1

POTENTIAL OF VEGETABLE OILS AS MICRO LUBRICATION / COOLING MEDIUM FOR SQL- GRINDING antifoaming agent and antiwear characteristics were used for the investigation.

The present work investigates the effectiveness of vegetable oils as MWF in grinding of hardened AISI 52100 steel under small quantity lubrication (SQL) mode.

2 POTENTIAL OF VEGETABLE OILS AS MICRO LUBRICATION / COOLING MEDIUM FOR SQL- GRINDING antifoaming agent and antiwear characteristics were used for the investigation. It was observed by them that the use of sunflower oil could reduce the thrust force to a significant amount. The present work investigates the effectiveness of vegetable oils as MWF in grinding of hardened AISI steel under small quantity lubrication (SQL) mode. Palm oil, and sunflower oil were selected and their performance during grinding were compared with that of synthetic soluble oil under SQL environment by analyzing G- ratio, grinding force and transverse surface roughness. All the selected oils were initially characterized on wetting ability, and lubricity. Later on grinding experiments were conducted under plunge mode on a reciprocating type surface grinding machine and results were co-related. 2 Experimental Details 2.1 Characterization of oils The role of a cutting fluid in grinding is to act as cooling and lubricating medium, keeping the surface separate and remain adequately stable to guarantee constant behavior. Wettability and lubricity are two important parameters that determine the effectiveness of a cutting fluid in providing proper cooling and lubrication in the grinding zone. The selected vegetable oils were tested for their wetting ability on a wettability analyser (Make: GBX Instruments, France, Model: GBX- Digidrop) which works based on modular contact angle technology(fig. 1). Here the advancing and receding contact angle of a droplet were measured with the help of a droplet injector, light source and a camera. Two different substrates made of AISI steel and alumina were used for the above measurement. Similarly lubrication ability of the selected oils was investigated on a ball on disc tribometer. Since the grinding of AISI steel was performed by an alumina wheel, a hardened AISI steel disc and an alumina ball were used for tribology test. The disc was made to rotate against the ball for five minutes under a normal load of 50N. The sliding speed was maintained at 3m/s and the friction coefficient between the sliding surfaces were monitored. Results of the tribo test and wetting experiment are tabulated in Table 1. Table 1 Characteristics of the elected MWFs used for SQL grinding Type of coolant/ lubricant Avg. coe. of friction at steel- alumina interface Wetting angle (degrees) on on steel alumina Soluble oil Sunflower oil Palm oil Performance evaluation of oils in SQLgrinding The grinding experiments were conducted on a reciprocating type surface grinding machine. Figure 2 shows the experimental setup and the experimental conditions are briefed in table 2. A flat surface grinding was carried out in plunge mode on a hardened AISI steel plate using an alumina wheel. Grinding was continued for a total number of 50 passes under all conditions and during each pass both tangential and normal component of force were monitored online using a piezo electric dynamometer (Make: Kistler, Switzerland, Model- 9257B). Grinding force alone doesn t give an overall idea about the effectiveness of a grinding process. It is to be interpreted with G- ratio, which is defined by rate of work-volume removed per unit rate of wheelvolume consumed. For the estimation of G-ratio a long run test (1000passes) was carried out. SQL flow rate was maintained at 500ml/hr and a constant down feed of 10µm was given. It was approximated that the radial wear of the wheel (avg. of 8 locations, 45 apart) is rectangular and wheel wear rate was calculated based on average depth of radial groove using a 1µm resolution dial indicator. Surface finish is an important parameter which is linked with the quality of ground surface, finally determining the product quality. Surface roughness was measured across the width of the job after 50 passes using a roughness tester (Make: Mahr, USA). Fig 1 Pictorial view of experimental set up: wetting angle measurement Fig 2 Pictorial view of experimental setup- SQL grinding 387-2

3 Table 2 Experimental conditions Machine Tool Work specimen specification Material Composition Size Grinding Wheel Specifications Technical Spec. Wheel dimensions Process Parameters Wheel speed(v c ) Table Speed (V w ) Depth of cut( a e ) No. of passes SQL Supply 3 Results and discussion Name: Reciprocating flat surface grinding machine Make: ALEX Machine Tools India Pvt. Ltd. Model: NH 500 Hardened AISI steel (C:0.92%, Mn:0.41%, Si: 0.26%, Cr:1.3%, S:0.04%, P:0.05%) 100mm 70mm 10mm A60K5V8 Φ200mm 25mm width; bore dia.: 50mm 25m/s 6m/min 5µm, 10µm & 20µm 50 for evaluationof force & 1000 for estimation of G- ratio Air pr.: 3 bar,mwfconsum. rate: 500ml/hr It is clearly evident from table 1 that both sunflower oil and palm oil could offer improved lubricity at the sliding interface of alumina ball and bearing steel disc. Sunflower oil was found to outperform palm oil and it could reduce the coefficient of friction by 30% with respect to soluble oil. In terms of wetting angle measurement on steel and alumina substrate, it can be observed from the table that sunflower oil wetted the surfaces the best. However it has shown a marginal improvement as compared to the wetting angle produced by soluble oil. In terms of wetting angle and coefficient of friction palm oil could be recognized as the weakest MWF agent. A recent study of the present research group (ManojKumar et al. 2013) clearly indicated that SQLsoluble oil has shown substantially better performance than flood- soluble environment. Therefore in the present study the result of flood- soluble oil is not included. Variation of grinding force components under dry and SQL environments are analysed. It is evident from the graphical representation of tangential force that for dry grinding after initial spark-in period the force steadily increased with a significant slope till 50 th pass, clearly indicating the progressive dulling of the grits. Small fluctuations of the force depict the dulling- resharpening- dulling cycles typically a grinding wheel is known to experience. With the application of the SQL- soluble oil the magnitude of the force got substantially reduced, which is due to the lubrication and cooling ability of the fluid resulting in substantial improvement in restoring grit sharpness. It is further observed that application of the vegetable oil was able to offer additional benefit in terms of reduction of the tangential force. Tangential force component is supposedly influenced by the lubrication ability of the MWF. Therefore the effect of lubrication and better wetting ability of sunflower oil was substantially pronounced in its out performance over its counterpart that is palm oil. Fig.3 (b) displays the trend of normal force variation with respect to number of passes also brings out a similar performance of sunflower oil relative to palm oil. (a) Fig. 3 Variation of (a) tangential and (b) normal force components with number of passes during SQL grinding of AISI steel using different fluids (b) 387-3

POTENTIAL OF VEGETABLE OILS AS MICRO LUBRICATION / COOLING MEDIUM FOR SQL- GRINDING Therefore it is evidently conclusive that sunflower did not just lubricate the interface but also protects the grit

A similar trend was observed in the case of normal force component also.

4 POTENTIAL OF VEGETABLE OILS AS MICRO LUBRICATION / COOLING MEDIUM FOR SQL- GRINDING Therefore it is evidently conclusive that sunflower did not just lubricate the interface but also protects the grit sharpness by its additional cooling capability in SQL mode. However to ensure the out performance of sunflower oil the experiment was repeated at different conditions, by varying down feed (Fig.4 (a) & (b)). It was observed that sunflower oil was able to achieve an average reduction of 45% in tangential force component in fine grinding and 26% in aggressive grinding when compared to soluble oil. A similar trend was observed in the case of normal force component also. Palm oil was able to produce lower tangential force than synthetic soluble oil at low down feed conditions but failed during aggressive grinding. At the same time average normal force was higher for palm oil under all working conditions. This may be due to the inability of palm oil to retain grit sharpness during the course of grinding. (a) Fig 4 Average value of (a) tangential and (b) normal force components under dry and different SQL environments. Fig 5 G ratio estimated for SQL grinding with different MWFs (b) Fig. 5 represents the estimated value of G- ratio during the grinding process using all the fluids. Sunflower was able to achieve a 6% improvement in Fig 6 Surface roughness generated while grinding with different MWFs underdifferent environment G-ratio than synthetic soluble oil and 15% than palm oil. A higher G-ratio obtained by sunflower oil indicates an improved machinabilty due to effective cooling and lubrication at the grinding zone. Transverse surface roughness which is measured across the width of the workpiece under all working condition is shown in Fig. 6. A better finish was observed in all SQL conditions except in the aggressive domain. Surface finish is a complex outcome of grindability of work material, retention of grit sharpness and chip flushing from the grinding zone. The difference in the values produced by SQLsoluble oil and SQL-veg. oil environment is too marginal to conclude a specific reason. A comparatively higher roughness value for sunflower can be an indication of the retention of grit sharpness during grinding

5 4 Conclusions The present investigation summarily indicates the effectiveness and outperformance of vegetable oil in SQL grinding. Following inferences could be conclusively drawn: Palm oil and sunflower oil were successfully delivered in SQL mode. Both offered good lubrication at the sliding interface of alumina ball and bearing steel disc.however, the later was found to be superior to other oils in terms of lubrication and wettability. Sunflower oil outperformed its counterparts in reducing both tangential and normal force components under all working conditions because of better retention of grit sharpness. A better G-ratio was achieved by using sunflower oil as grinding fluid under SQL mode which was followed by soluble oil and then palm oil. However, surface roughness produced by sunflower oil was marginally higher than that produced by other two oils, due to sharper cutting action of grits in course of grinding but was in acceptable range. References Alves, S.M. and Oliveira, J.F.G. (2006), Development of new cutting fluid for grinding process adjusting mechanical performance and environmental impact, Journal of Material Processing Technology, Vol.197, pp Khan, M.M.A., Mithu, M.A.H. and Dhar, N.R. (2009), Effects of minimum quantity lubrication on turning AISI 9310 alloy steel using vegetable oilbased cuttingfluid, Journal of Material Processing Technology, Vol.209, pp Kuram, E., Ozcelik, B., Demirbas, E. and Sik, E. (2010), Effects of the cutting fluid types and cutting parameters on surface roughness and thrust force, Proceedings of the WCE 2010, London, UK, Vol. II, June 30 July 2, ManojKumar., K and Ghosh., A. (2013), Small Quantity Lubrication (SQL) grinding of AISI steel using MWCNT dispersed nanofluid,international Conference on Precision, Meso, Micro and Nano Engineering(COPEN- 8),December 13-15, NIT Calicut, Sadeghi, M., Hadad, M., Tawakoli, T., Vesali, A. and Emami, M. (2010),An investigation on surface grinding of AISI 4140 hardened steel using minimum quantity lubrication-mql technique, International Journal of Material Forming,Vol. 3,pp Sharif, S., Yusof, N.M., Idris, M.H., Ahmad, Z.B., Sudin, I., Ripin, A. and MatZin, M.A.H. (2009), Feasibility study of using vegetable oil as a cutting lubricant through the use of minimum quantity lubrication during machining, Research Vol.78055, Department of Manufacturing and Industrial Engineering, Faculty of Mechanical Engineering, University Technology Malaysia. Shen, B., Shih, A.J. and Tung, S.C. (2008), Application of Nanofluids inminimum Quantity Lubrication Grinding, Tribology Transactions,Vol. 51, pp Silva, L., Bianchi, E., Catai, R., Fusse, R., França, T. and Aguiar, P.(2007), Analysis of surface integrity for minimum quantity lubricant- MQL in grinding, International Journal of Machine Tools and Manufacture, Vol. 47, pp Tawakoli, T., Hadad, M.J., Sadeghi, M.H., Daneshi, A., Stöckert, S. and Rasifard, A. (2009), An Experimental Investigation of the Effects of Workpiece and Grinding Parameters on Minimum QuantityLubrication MQL Grinding, International Journal of Machine Tools and Manufacture,Vol. 49, pp Wilfried J. Bartz(1998), Lubricants and the environment, Tribology International, Vol. 31, pp

Effect of the Cryogenic cooling on. Surface Quality of Ground AISI Steel

Effect of the Cryogenic cooling on Surface Quality of Ground AISI 52100 Steel P. Prudvi Reddy 1, A.Ghosh 2* 1 Dept. of Mech. Engg., Indian Institute of Technology Madras, Chennai, 600036, pprudvi108@gmail.com