Experimental Determination of Cutting Power for Turning and Material Removal Rate for Drilling of AA 6061-T6 Using Vegetable Oils as Cutting Fluid

e raw and modi�ed versions of two nonedible vegetable oils, Pongam (Pogammia pinnata) and Jatropha (Jatropha curcas), and a commercially available brandedmineral oil are used as straight cutting �uids for turningAA6061 to assess cutting forces.Minimum quantity lubrication is utili�ed for the supply of cutting �uids. Cutting and thrust forces are measured. Cutting power is determined for various cutting speeds, depths of cut, and feed rates. Also, drilling is performed on the material to understand the material removal rate (MRR) under these oils. e performances of vegetable oils are compared to mineral oil. A noticeable reduction in cutting forces is observed under the Jatropha family of oils compared to mineral oil. Further, better material removal rate is seen under both the vegetable oils and their versions compared to under petroleum oil for the range of thrust forces.


Introduction
Cutting forces are considered as important parameters in turning operation, and they dictate the power required for machining [1].e cutting forces in�uence the deformation of the workpiece machined its dimensional accuracy, chip formation, tool wear, surface roughness, and machining system stability.Higher magnitudes of forces lead to distortion in workpiece, low dimensional accuracy, faster tool wear, poor surface �nish, and undesirable vibrations.Cutting forces generated mainly depend on the depth of cut, cutting speed and type of cutting �uid.As the depth of cut increases, magnitudes of forces also increase.However, increase in cutting speeds reduces the magnitude of forces.Further, cutting �uids with high lubricity, high �lm boiling point, and quick wetting and spreading and friction reduction at extreme pressure properties reduce cutting forces signi�cantly [2].
Metalworking �uids are extensively used in machining operations.ere are several types of metalworking �uids (MWFs), which may be used to carry out such tasks [3].e ma�ority of the MWFs are mineral oil-based �uids.ese �uids increase productivity and the quality of manufacturing operations by cooling and lubricating during metal cutting processes [4].e consumption of MWFs is increasing in machining industry due to their advantages.As cutting �uids are complex in their composition, they may be irritant or allergic.Even microbial toxins are generated by bacteria and fungi present, particularly in water-soluble cutting �uids [5], which are more harmful to the operators.
To overcome these challenges, various alternatives to petroleum-based MWFs are currently being explored by scientists and tribologists.Such alternatives include synthetic lubricants, solid lubricants, and vegetable-based lubricants.In general, vegetable oils are highly attractive substitutes for petroleum-based oils because they are environmentally friendly, renewable, less toxic, and readily biodegradable [6,7].Consequently, currently, vegetable-based oils are more potential candidates for the use in industry as MWFs.Many investigations are in progress to develop new bio-based cutting �uids based on various vegetable oils available around the world.e performance of soybean, canola, palm, sun�ower, and ground nut oils are evaluated as cutting �uids for machining different materials.Turning, drilling, reaming, and tapping operations on austenitic stainless steel and other four materials were evaluated using vegetable-based formulations [8].e results, on austenitic steel revealed that the cutting force under vegetable oils and esters is about 20% lower compared to reference mineral oils.Further, it is reported that about 40% increase in tool life under vegetable oils/ester modes of lubrication.Lower surface roughness, strain hardening, and thickness of the plastically deformed subsurface layer and better part accuracy are reported for a vegetable-based cutting �uid tested for reaming and tapping operations [9].Cutting �uid formulations based on canola oil, soybean oil, and a TMP ester were made and were evaluated under tapping torque tests on 1018 cold rolled steel [10].It is reported that all the bio-based oils exhibited about 12-14% increase in tapping torque efficiency relative to the reference soluble oil.However, Soy-based metalworking �uid had slightly higher tapping torque efficiency in the semisynthetic form compared to others.
As cutting �uids, ground nut and Shea butter oils generated lower cutting forces and coefficient friction while turning mild steel, aluminum, and copper workpieces [11].�etter surface �nish is also reported under these oils.A formulated cutting �uid of canola with 8% extreme pressure additive showed comparable turning forces with mineral oils.About 61% drop in surface roughness values are reported compared to commercial mineral oil.Further, about 10% drop in tool wear is seen while turning AISI 304 L under canola oil [12].Sun�ower and canola-oil based cutting �uids showed better surface �nish and produced lower cutting and feed forces while turning AISI 304 L [13].Soybean, canola, and palm-oil based soluble cutting �uids are used for milling.About 10% lower surface roughness values reported comparable to �ank wear are seen under these formulated oils compared to mineral oil [14].
e motive of the present work is to bring out the enormous potential of vegetable oils to be used in manufacturing sector as straight cutting oils or lubricants.is has gained more importance in the light of the recent restrictions made by world leaders like OSHA, HOSH, EPA, and so forth, where they have suggested to come out with replacements for mineral oils, that are the most environmentally friendly and also are depleting.Also, there is a large consumption of cutting oils/lubricants for the manufacturing sector.
In the present study, the raw and modi�ed versions of two nonedible vegetable oils, Pongam (Pongammia pinnata) and Jatropha (Jatropha curcass), and a commericially available branded mineral oil are used as straight cutting �uids.Turning and drilling of AA 6061 under these oils are chosen for the study.Cutting and thrust forces are measured for various cutting speeds, depth of cut, and feed.Cutting power is determined for turning the material.Further, drilling is performed on the material to assess the material removal rate (MRR) under these oils for various thrust forces.e results obtained are compared to the results under mineral oil.

Experiments
���� �i� �o�i�cation� e raw vegetable oils have certain limitations like low thermooxidative stability [15].ese problems are addressed by various methods, namely, reformulation of additives, chemical modi�cations, and genetic modi�cation of the oil seed [16].In the present work, chemical modi�cation methods such as epoxidation [17] and transesteri�cation [18] are used to modify the structure of two raw oils.A�er the modi�cations, their polyunsaturated C=C bonds are eliminated in the oil structure, and the thermooxidative stability, the resistance of a lubricant to molecular breakdown or molecular rearrangement at elevated temperature in the absence/presence of oxygen, is enhanced.
e MQL circuit (Figure 1) consists of an air compressor, mixing chamber, nozzle, and three pressure gauges.A nozzle of 2 mm is used for the experiments.Compressed air at 3 bar pressure is mixed with oil in the mixing chamber.e mist formed from the chamber is then fed in between cutting tool and workpiece through the nozzle.
Experiments are conducted under mineral, raw, and modi�ed versions of the two vegetable oils as straight cutting oils for various cutting speeds (60, 90, and 140 m/min), depths of cuts (0.5, 1.0, and 1.5 mm), and feeds of 0.1 mm/rev, 0.18 mm/rev, and 0.25 mm/rev.e cutting forces are measured using Kistler lathe tool dynamometer (Figure 2).e forces are used to determine cutting power for turning.
Drilling is performed on AA 6061 sheets using HSS drill tool.Experiments are conducted for a constant spindle speed of 2625 rpm (maximum available speed).e time for drilling a hole is noted for thrust forces of 112 N, 138 N, 172 N, and 182 N under mineral, raw, and modi�ed versions of the two vegetable oils as cutting �uids.e thrust forces are measured using a drill tool dynamometer.

Results and Discussion
3.1.Cutting Power.Cutting power required for machining provides the necessary input to understand the capacity of the drive.Cutting �uid with better lubrication capabilities reduces the power requirements.
Experimentally measured cutting forces for various cutting speeds, depths of cut, and feed are used to calculate the cutting power for turning AA 6061 under mineral and different vegetable oils and their versions (Table 1).Further, the results are also represented as three-dimensional pictures.e desirable conditions for turning AA 6061 under vegetable oil (raw and modi�ed) are compared to mineral oil.An expected linear raise in cutting power is seen with an increase  in cutting speeds and depths of cut [19].Increase in cutting power is marginal for increase in cutting speed.However, it is signi�cant with higher depths of cuts.Figure 3 shows the cutting power distribution.Figure 3 through to Figure 6 are the plots with maximum drop in cutting power for Pongam and its versions.Figure 6 through to Figure 8 are for Jatropha and its versions.

Comparison of Pongam with Mineral
Oil. Pongam raw oil and its modi�ed versions show lower cutting power compared to mineral oil for the complete range of cutting speeds, depths of cut, and feed.Around 25% drop in cutting power for the feed 0.1 mm/rev and 0.5 mm depth of cut is seen under PRO (Figures 3 and 4).is drop is the maximum compared to other combinations of feed and depths of cut.EPRO exhibits maximum of 20% lower cutting power for 0.1 mm/rev of feed and 1 mm depths of cut compared to MRO (Figure 5).About 28% drop in cutting power for feeds 0.1 mm/rev and 0.5 mm depth of cut is seen under EPME compared to petroleum oil (Figure 6).On the other hand, a marginal increase in cutting power is seen for higher feed and depths of cut.

Comparison of Jatropha with Mineral Oil. Similar to
Pongam family of oils, Jatropha raw oil and its modi�ed versions also show lower cutting power compared to mineral oil for the complete range of cutting speeds, depths of cut, and feeds.A maximum of 30% drop in cutting power is seen under JRO for the feed of 0.25 mm/rev and depth of cut 1 mm compared to mineral oil (Figure 7).Further, 10% constant drop in cutting power is observed for the other two depths of cut and feeds compared to petroleum oil.About 20% reduction in cutting power under EJRO for feed 0.25 mm/rev and depth of cut 1mm compared to MRO (Figure 8).Under EJME, about 25% reduction in cutting power is seen for all the depths of cut and feed range except for feed 0.25 mm/rev and depth of cut 1.5 mm (Figure 9).e drop in cutting power for turning under all the types of vegetable oils can be attributed to their polar nature and viscosity properties.Signi�cant power reductions under vegetable oils can be due to the fact that, the thin surface �lm that develops in boundary lubrication is formed by  the adsorption of polar compounds at the metal surface of the mating pair or by chemical reaction of the lubricant at the surface.Since, boundary lubrication by fatty acids is associated with the adsorption of the acid by dipolar attraction at the surface, they are capable of reducing the friction between the surfaces [20].Jatropha versions exhibit noticeable power reductions at very high cutting speeds and depths of cut.is is due to high Oleic acid content [21] in the oil, higher viscosity index, and higher thermal conductivity of Jatropha compared to Pongam as well as mineral oil.

Drilling.
In this segment, material removal rate under the two vegetable oils and their modi�ed versions are analysed and compared to mineral oil for the range of thrust force (112 N to 180 N).

Material Removal Rate (MRR).
It is the volume of material removed/drilled out from the workpiece per unit time.It depends on the material, thrust force, feed, cutting speed, and cutting �uid.In drilling, high material removal rate and long drill life are essential to increase productivity.To achieve the desired MRR, high feed per revolution and cutting speed are required [22�.Further, a cutting �uid with good lubrication property produces higher rate of material removal.
Higher material removal is seen under both the vegetable oils and their versions compared to under mineral oil for  the range of thrust forces.is could be clearly seen from Figure 10 that, say, for the thrust force of 172 N, about 20% increase in MRR is observed under Pongam family (Figure 11) compared to under mineral oil.Similarly, under Jatropha family, about 40% increase in MRR is noticed.Interestingly, EJME offered the best MRR compared to all other oils tested with 50% increased MRR (Figure 12).It is attributed to the better lubrication capability of the oil.
e epoxidized methyl ester versions of both oils are seem to be the better cutting �uid to drilling AA 6061 as both of them show higher material removal property.

Conclusions
Pongam and Jatropha oils and their versions are better cutting �uids in terms of lower cutting forces and power

F 3 :
t h o f c u t ( m m ) C u tt in g sp ee d (m /m in ) Variation of cutting power with cutting speed and depth of cut under MRO.

1 F 4 :
e p t h o f c u t ( m m ) B : C u t t i n g s p e e d ( m / m i n ) Variation of cutting power with cutting speed and depth of cut under PRO.

F 5 :
e p t h o f c u t ( m m ) B : C u t t i n g s p e e d ( m / m i n Variation of cutting power with cutting speed and depth of cut under EPRO.

1 F 6 :
t h o f c u t ( m m ) C u t t i n g s p e e d ( m / m i n ) t h o f c u t ( m m ) C u t t i n g s p e e d ( m / m i n ) Variation of cutting power with cutting speed and depth of cut under EPME.

F 7 :
e p t h o f c u t ( m m ) B : C u t t i n g s p e e d ( m / m i n ) Variation of cutting power with cutting speed and depth of cut under JRO.

F 8 :
t h o f c u t ( m m ) C u tt in g s p e e d ( m / m in ) Variation of cutting power with cutting speed and depth of cut under EJRO.

F 9 :F 10 :
t h o f c u t ( m m ) C u tt ti n g sp ee d (m /m in ) Variation of cutting power with cutting speed and depth of cut under EJME.Variation of material removal rate with thrust force for various oils.

F 11 :
Variation of material removal rate with thrust force for Pongam family.

F 12 :
Variation of material removal rate with thrust force for Jatropha family.
T 1: Cutting power generated under various oils for different feed, depths of cut, and cutting speeds.