CHAPTER 6 FORMULATION OF A VEGETABLE OIL BASED CUTTING FLUID...

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CHAPTER 6

FORMULATION OF A VEGETABLE OIL BASED CUTTING FLUID FOR

HARD TURNING WITH MINIMAL FLUID APPLICATION

6.1 INTRODUCTION

Performance enhancers for increasing chip curl, improving rake face

lubrication and increasing extraction of heat from the cutting tool are discussed in

the previous sections. An attempt was made to develop a cutting fluid based on

vegetable oil and this section presents information on issues related to the use of

vegetable oils as metal cutting fluids, the procedure for formulating a cutting fluid

with coconut oil as the base and details of the cutting experiments conducted to

evaluate the performance of the cutting fluid formulated for hard turning with

minimal fluid application.

It is reported that cutting fluids based on coconut oil offered better cutting

performance when compared to mineral oil based cutting fluids. As it is 100%

biodegradable, it does not possess any problems connected with disposal. It is

highly environment and people friendly and causes no skin problems to workers

exposed to it. It has got high oxidative and thermal stability. The long chain

molecules of coconut oil are dipolar in nature and can create a dense,

homogeneous and strong lubricating film on the contact surfaces that can absorb

high pressures and offer better lubrication.

6.2 FORMULATION OF COCONUT OIL BASED CUTTING FLUID

The work reported by Varadarajan et al. (2000) was used as the basis for

formulating a cutting fluid with coconut oil as the base. The formulation acted as

an oil in water emulsion. The ingredients of the cutting fluid are presented in Table

6.1.

Oleic acid is an unsaturated fatty acid which is used as an emulsifying or

solubilizing agent. Besides serving as an agent for improving the lubricity of the

cutting fluid, it also acts as friction modifier for lowering the friction coefficient.

In water soluble cutting fluids, triethanol amine is used to provide the alkalinity

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needed to protect against rusting and it acts as an anti-oxidant. It also controls the

evaporation rate of water in cutting fluid.

Table 6.1 Composition of the concentrate

Sl.No Content Percentage by volume

1 Coconut Oil 40%

2 Oleic Acid 40%

3 Triethanol Amine 20%

Coconut oil based concentrate was formulated by mixing coconut oil with Oleic

acid and Triethanol Amine in the ratio of 2:2:1 respectively. 40 cc of coconut oil was

taken in a beaker and 40 cc of Oleic acid was added to it slowly in four steps. The

mixture was stirred thoroughly using a mechanical stirrer and when the mixture

became a homogeneous liquid, 20 cc of Triethanol Amine was added and stirred

thoroughly so as to get a homogeneous mixture which can dissolve in water in all

proportions and functions as oil in water emulsion. The oil in water emulsion

prepared out of the concentrate was subjected to emulsion stability test as per IS 1448

specification.

6.2.1 Emulsion stability test as per IS 1448

Following procedure was adopted to test the stability of the emulsion as per

IS 1448.

Step 1:

A CaSO4 solution of total hardness equivalent to 405ppm was prepaid by

dissolving 0.688gm of CaSO4 per liter of distilled water.

Step 2:

Eight emulsion samples were prepared as shown in the Table 6.2. The

requisite quantity of the concentrate was taken in a hypodermic syringe. The

corresponding quantity of water was taken in a 150 ml measuring flask which was

kept stirred using a stirrer so that a vortex was formed. The oil was poured in to the

vortex thus formed. The stirring was continued for 2 more minutes after the last

drop of oil was transferred. All the samples were allowed to stand for 48 hours and

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evaluated on the basis of separation, frothing, homogeneity and coloration. There

was no trace of oil separation in any one of the 8 samples prepared and this is an

indication of the stability emulsion as per IS 1448 specifications.

Table 6.2 Emulsion ratios and the corresponding proportions of water and

concentrate

Sample No. 1 2 3 4 5 6 7 8

Emulsion ratio 5:1 10:1 15:1 20:1 25:1 30:1 50:1 80:1

Test water (ml) 150 200 180 200 200 180 200 240

Concentrate

(ml) 30 20 12 10 8 6 4 3

6.2.2 Characterization of the concentrate

Physical properties of the concentrate such as density, viscosity, pH value

and refractive index were determined experimentally and summarized in Table 6.3

Table 6.3 Physical properties of the concentrate

Properties Value

Viscosity at 40oC (centipoises) 83.5

Specific gravity (kg/m3) 0.933

pH value 7.07

Fuming point (oC) 185

Refractive index 1.474

6.3 FEASIBILITIES STUDIES

It was decided to evaluate the feasibility of the cutting fluid formulation for

hard turning with minimal fluid application. Cutting experiments were conducted

on a Kirloskar Turn master- 35 lathe. AISI 4340 steel with a hardness of 45 HRC

was used as the work material. Bars of 70mm in diameter and 350 mm in length

were used in this investigation. Multicoated hard metal inserts with sculptured rake

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face geometry with a specification SNMG 120408 of Tague Tec was used in the

investigation. The tool holder had a specification of PSBNR 2525M12. The

minimal fluid application system used in the previous experiments was used in the

present investigation. Cutting experiments were conducted to compare the

performance of the coconut oil based cutting fluid formulation with a commercial

mineral based cutting fluid and pure coconut oil during hard turning with minimal

fluid application. This was accomplished by conducting a variable speed test, a

variable speed test and a tool life test. The fluid application parameters were kept

at values shown in Table 6.4.

Table 6.4 Values of fluid application parameters kept constant

Fluid application parameter Values

Rate of fluid application, Q 5ml/min

Pressure of the fluid injector, P 80 Bar

Frequency of pulsing, N 300 pulses/min

Percentage of concentrate, C 20%+rest water

The depth of cut was maintained as 1.25 mm and the time of cut was

maintained as 60 seconds for the variable speed test and the variable feed test. The

cutting force was measured using a Kistler tool force dynamometer, surface

roughness was measured using a stylus type surface meter (Perthen Make) and tool

flank was measured using a tool maker’s microscope and cutting temperature was

measured using an extrapolative technique (Varadarajan et al., 2000) based on

finite element analysis as described early.

The feed was kept at 0.1 mm/rev during the variable speed test and the

cutting velocity was varied from 80 to 120 m/min at five intervals. The cutting

velocity was kept at 80 m/min, and the feed was varied from 0.04 to 0.08 mm/rev

at five equal levels. During the tool life test cutting velocity was kept at 80 m/min,

feed at 1 mm/rev and depth of cut at 1.25 mm. Figure 6.1 presents a photograph of

the experimental set up.

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Figure 6.1 Photograph of the experimental set up

6.3.1 Results and Discussion

Figures 6.2 (a) to 6.2 (d) present the variation of cutting force, cutting

temperature, surface roughness and tool chip contact length as a function of cutting

velocity. The variation of cutting force, cutting temperature, surface roughness

and tool chip contact length with feed are presented in Figures 6.3 (a) to 6.3 (d)

respectively.

Low cutting forces and tool-chip contact lengths were observed when raw

coconut oil was used as the cutting fluid when compared to that observed during

the application of mineral oil based cutting fluid and the coconut oil based cutting

fluid formulated as evident from Figures 6.2 (a), 6.2 (d), 6.3 (a) and 6.3 (d).

Coconut oil has high thermal stability and the long chained molecules of coconut

oil are dipolar in nature and can create a dense, homogeneous and strong

lubricating film in the contact zones. The film can absorb high pressure and offer

better lubrication resulting in reduction in tool-chip contact length and lower

cutting force. But it was found that raw coconut oil could not bring forth low

cutting temperatures as shown in Figure 6.2(b) and Figure 6.3 (b). This is due its

low cooling ability. It was observed that the performance of mineral oil based

cutting fluid was at par with that of coconut oil based cutting fluid in this aspect as

both of them contained lubricant (oil) as well as coolant (water).

WORKPIECE

NOZZLE AT THE

TOOL WORK INTERFACE

TOOL HOLDER WITH INSERT

TOOL WORK

THERMOCOUPL

E

KISTLER DYNAMOMETE

R

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Figure 6.2 (a) Variation of cutting force as a function of cutting velocity during the

application of mineral oil based cutting fluid, coconut oil based cutting fluid and

raw coconut oil.

Figure 6.2 (b) Variation of cutting temperature as a function of cutting velocity

during the application of mineral oil based cutting fluid, coconut oil based cutting

fluid and raw coconut oil.

0

20

40

60

80

100

120

140

160

180

80 90 100 110 120

Cu

ttin

g Fo

rce

(Fz

), N

Cutting Velocity (m/min)

Coconut oil based cutting fluid

Raw cocnut oil

Mineral oil based cutting fluid

200

220

240

260

280

300

320

80 90 100 110 120

Cu

ttin

g Te

mp

era

ture

(T)

, oC

Cutting velocity (m/min)


Raw cocnut oil


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Figure 6.2 (c) Variation of surface roughness as a function of cutting velocity

during the application of mineral oil based cutting fluid, coconut oil based cutting

fluid and raw coconut oil.

Figure 6.2 (d) Variation of cutting force as a function of cutting velocity during the


raw coconut oil.

0

0.5

1

1.5

2

2.5

80 90 100 110 120

Surf

ace

Ro

ugn

ess

(R

a), µ

m



Raw cocnut oil


0

0.05

0.1

0.15

0.2

0.25

0.3

80 90 100 110 120 Too

l Ch

ip C

on

tact

len

gth

(Lc

), m

m



Raw cocnut oil


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Figure 6.3 (a) Variation of cutting force as a function of feed rate during the


raw coconut oil.

Figure 6.3 (b) Variation of cutting temperature as a function of feed rate during the


raw coconut oil.

0

50

100

150

200

250

300

350

400

0.04 0.05 0.06 0.07 0.08

Cu

ttin

g Fo

rce

( Fz

), N

Feed (mm/rev)


Raw cocnut oil


0

50

100

150

200

250

300

0.04 0.05 0.06 0.07 0.08

Cu

ttin

g Te

mp

era

ture

(Tc

), o

C

Feed (mm/rev)


Raw cocnut oil


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Figure 6.3 (c) Variation of surface roughness as a function of feed rate during the


raw coconut oil.

Figure 6.3 (d) Variation tool chip contact length as a function of feed rate during

the application of mineral oil based cutting fluid, coconut oil based cutting fluid

and raw coconut oil.

0

0.5

1

1.5

2

2.5

0.04 0.05 0.06 0.07 0.08

Surf

ace

Ro

ugh

ne

ss (

Ra)

, µm

Feed (mm/rev)


Raw cocnut oil


0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.04 0.05 0.06 0.07 0.08 Too

l Ch

ip C

on

tact

len

gth

(Lc

), m

m

Feed (mm/rev)


Raw cocnut oil


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Figure 6.4 Variations of flank wear with time during turning with minimal fluid

application using mineral oil based cutting fluid, coconut oil based cutting fluid

and raw coconut oil.

Figure 6.5 (a) SEM photograph of tool wear when coconut oil based cutting fluid

was used.

Figure 6.5 (b) SEM photograph of tool wear when raw coconut oil was used as

cutting fluid.

0

0.05

0.1

0.15

0.2

0.25

30 60 90 120 150

Flan

k W

ear

(V

b),

mm

Time (Sec)


Raw cocnut oil


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Figure 6.5 (c) SEM photograph of tool wear when mineral oil based cutting fluid

was used.

Figure 6.6 (a) Chip microgram during the application of coconut oil based cutting

fluid (V=80 m/min, f=1 mm/rev, d=1.25 mm)

Figure 6.6 (b) Chip microgram during the application of raw coconut oil as cutting


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Figure 6.6 (c) Chip microgram during the application of mineral oil based cutting


Figures 6.2 (c) and 6.3 (c) clearly show that the application of coconut oil

based cutting fluid resulted in the lowest values of surface roughness. This is due

to the superiority of the lubricating ability of the coconut oil based cutting fluid

when compared to that of mineral oil based cutting fluid on account of its structure

and thermal stability. Reduction in cutting temperature and cutting force brought

forth by better lubrication at the tool work interface reduced the tool wear and

hence improved the surface finish. The superiority of coconut oil based cutting

fluid was established further by the results of tool life test. The tool wear was the

least during the application of coconut oil based cutting fluid during the whole

length of tool life test (Figure 6.4). Moreover, SEM photographs (Figure 6.5 (a),

(b) and (c)) of worn inserts indicated less damage to the cutting edge when coconut

oil based cutting fluid and raw coconut oil were used.

Table 6.5 Thickness of chips collected

CHIP THICKNESS, tc (mm)

Coconut oil based cutting fluid 0.19

Raw coconut oil as cutting fluid 0.15

Conventional mineral oil based cutting fluid 0.26

Chip microgram during the application of coconut oil based cutting fluid

is shown in Figure 6.6 (a). The chip micrograph during the application of raw

coconut oil is shown in Figure 6.6 (b). Figure 6.6 (c) presents the chip microgram

when mineral oil based cutting fluid was used under the same cutting conditions.

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Thickness of the chips collected during experiments was measured using tool

maker’s microscope and is presented in Table 6.5. The chip thickness was 0.26

mm during the application of mineral oil based cutting fluid where as it was

0.19mm during the application of coconut oil based cutting fluid. It was as low as

0.15mm when raw coconut oil was used as cutting fluid. It was also observed that

the chip sections contained less signs of distortions when the raw coconut oil was

used as well as when coconut based cutting fluid was used. Chip thickness is an

index of the frictional conditions at the tool chip interface. Better the rake face

lubrication, thinner will be the chips and lesser will be the deformation and

damages on its cross section.

6.4 EFFECT OF PERCENTAGE OF CONCENTRATE ON CUTTING

PERFORMANCE

It was decided to study the effect of the percentage of concentrate in the

cutting fluid on cutting performance. Accordingly the percentage of the

concentrate was varied at four levels as shown in Table 6.6. A tool life test was

conducted using multicoated hard metal inserts with sculptured rake face with a

specification SNMG 120408. AISI 4340 steel with a hardness of 45 HRC was used

as work material and the cutting experiments were carried out on a Kirloskar Turn

master-35 lathe. The cutting velocity was kept at 80 m/min, feed at 1 mm/rev and

depth of cut at 1.25 mm. The fluid application parameters were maintained at

values as shown in Table 6.7. Flank wear was measured at an interval of 30

seconds using a tool maker’s microscope and the results are presented in Figure

6.7.

Table 6.6 Percentage of concentration in the cutting fluid

Level % of concentrate % of water

1 10 90

2 20 80

3 30 70

4 40 60

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Table 6.7 Values of fluid application parameters that were kept constant

Fluid application parameters Values

Rate of fluid application, Q 5ml/min

Pressure of the fluid injector, P 80 bar

Frequency of pulsing, F 300 pulses/min

Fig. 6.7 Variation of tool wears during tool life test

Highest tool wear values are observed when the cutting fluid consisted of

10% concentrate and the rest water. When the cutting fluid composition was at

level 2, ie 20% concentrate and the rest water, there was a reduction in the tool

wear in the whole range. The tool wear characteristics marked still lower values

when the cutting fluid composition was kept at level 3 (ie, 30% concentrate + 90%

water). But when the percentage of concentrate was further increased to 40% there

was only marginal reduction in the wear characteristics. Tool wear is decided by

the combined effect of cooling and lubricating abilities of the cutting fluid. When

the percentage of concentrate is more, the lubricating ability of the cutting fluid

increases but its cooling ability comes down as the percentage of water is reduced.

The cutting fluid will offer its best when there is a good balance between its

lubricating and cooling abilities. It appears that when the percentage of concentrate

was kept at 30% there is a good balance between its lubricating as well as cooling

0

0.02

0.04

0.06

0.08

0.1

0.12

30 60 90 120 150

Too

l We

ar (

mm

)

Time (Sec)

10%

20%

30%

40%

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ability. When the percentage of the concentrate was increased to 40% there was

not much improvement in the wear characteristics which is in support of the

concept mentioned above. Hence the percentage of concentrate in the cutting fluid

may be maintained at 30% that will lead to better tool wear characteristic and at

the same time can fetch a saving of 10% in the use of concentrate.

6.5 SUMMARY

A cutting fluid was formulated with coconut oil as the base which can act as

an oil in water emulsion during turning of hardened AISI 4340 steel with minimal

fluid application. The performance of the new cutting fluid was compared with

that of a conventional mineral oil based cutting fluid and raw coconut oil by

conducting cutting experiments. It was observed that the coconut oil based cutting

fluid offered better cutting performance interns of low tool wear, low surface

roughness, low cutting force and low cutting temperature when compared to

mineral oil based cutting fluid and raw coconut oil. It was also observed that the

percentage of concentrate in the cutting fluid can be maintained as 30% to achieve

better cutting performance during turning of hardened AISI 4340 steel with

minimal fluid application. Cutting fluid with coconut oil as the base is

environment as well as human friendly. It is biodegradable in nature and hence

free from problems associated with disposal. Coconut oil based cutting fluid can

fetch saving in terms of foreign exchange as it does not need mineral oils which

are to be imported.

The government can introduce legislation encouraging the use of cutting

fluids based on vegetable oils like coconut oil which offers better cutting

performance and at the same time free from environment related problems and

problems related to storage and disposal. Moreover, use of cutting fluids based on

vegetable oils can bring forth considerable reduction in the quantities of petroleum

products imported.

CHAPTER 6 FORMULATION OF A VEGETABLE OIL BASED CUTTING FLUID...

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