j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 9 ( 2 0 0 9 ) 900–909

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Determining the influence of cutting fluids on tool wear andsurface roughness during turning of AISI 304austenitic stainless steel

M. Anthony Xavior ∗, M. AdithanMechanical Engineering, VIT University, Vellore 632014, Tamil Nadu, India

a r t i c l e i n f o

Article history:

Received 16 January 2007

Received in revised form

23 January 2008

Accepted 27 February 2008

Keywords:

Turning

a b s t r a c t

Knowledge of the performance of cutting fluids in machining different work materials is

of critical importance in order to improve the efficiency of any machining process. The

efficiency can be evaluated based on certain process parameters such as flank wear, surface

roughness on the work piece, cutting forces developed, temperature developed at the tool

chip interface, etc. The objective of this work is to determine the influence of cutting fluids

on tool wear and surface roughness during turning of AISI 304 with carbide tool. Further

an attempt has been made to identify the influence of coconut oil in reducing the tool

wear and surface roughness during turning process. The performance of coconut oil is also

being compared with another two cutting fluids namely an emulsion and a neat cutting oil

Tool wear

Surface roughness

Coconut oil

(immiscible with water). The results indicated that in general, coconut oil performed better

than the other two cutting fluids in reducing the tool wear and improving the surface finish.

Coconut oil has been used as one of the cutting fluids in this work because of its thermal

and oxidative stability which is being comparable to other vegetable-based cutting fluids

used in the metal cutting industry.

rotating cylindrical work piece. The material removed, called

1. Introduction

AISI 304 steel finds its application in air craft fittings,aerospace components such as bushings, shafts, valves, spe-cial screws, cryogenic vessels and components for severechemical environments. They were also being used for weldedconstruction in aerospace structural components. Most of thecomponents require certain machining in different machines.During machining of AISI 304 the operators encounter certaindifficulties such as premature tool failure and poor surfacefinish due to high temperature at tool–work piece interface. In

order to overcome these difficulties, the artisans working insmall and tiny industries started using coconut oil as a cut-ting fluid for machining. It has been found that coconut oil

∗ Corresponding author. Tel.: +91 416 2202228/43091; fax: +91 416 22430E-mail address: Xavior anto@hotmail.com (M.A. Xavior).

0924-0136/$ – see front matter © 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.jmatprotec.2008.02.068

© 2008 Elsevier B.V. All rights reserved.

extended the tool life with a better surface finish for machin-ing at low and medium cutting speed. In this context, thisstudy becomes necessary to understand the theory behind theperformance of coconut oil during the machining of AISI 304material.

1.1. Machining

Turning is a widely used machining process in which a single-point cutting tool removes material from the surface of a

92/40411.

chip, slides on the face of tool, known as tool rake face, result-ing in high normal and shear stresses and, moreover, to ahigh coefficient of friction during chip formation. Most of

j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 9 ( 2 0 0 9 ) 900–909 901

Table 1 – Typical chemical composition for the AISI 304

C 0.05487Si 0.64Mn 1.66Cr 18.2Ni 9.11Mo 0.092Cu 0.14Ti 0.006V 0.046W 0.048Co 0.40Nb 0.013Pb 0.015Fe 69.7

twtwapwaseidIrFc(

ssvnfmwntiepedK

Table 2 – Typical physical and thermal properties for theAISI 304

Parameters Unit Value

Density kg/m3 8000Elastic modulus GPa 193Poisson’s ratio – 0.3

coolant (Taylor, 1907). Cutting fluids improve the efficiencyof machining in terms of increased tool life, improved sur-

he mechanical energy used to form the chip becomes heat,hich generates high temperatures in the cutting region. Due

o the fact that, higher the tool temperature, the faster theear, the use of cutting fluids in machining processes has,s its main goal, the reduction of the cutting region tem-erature, either through lubrication and reduction of frictionear, and through a combination of these functions. Amongll the types of wear, flank wear affects the work piece dimen-ion, as well as quality of surface finish obtained, to a largextent. Asibu (1985) found that flank wear results in changesn the mechanics of the cutting process, an increased ten-ency for chatter and changes in the dimension of the product.

n practice, the extent of flank wear is used as the crite-ia in determining the tool life (Byrd and Ferguson, 1978).lank wear may be due to adhesive wear or abrasive wearaused by the hard second phases in the work materialRamalingam and Wright, 1981).

In machining of parts, surface quality is one of the mostpecified customer requirements where major indication ofurface quality on machined parts is the surface roughnessalue. Noordin et al. (2001) determined that the surface rough-ess is dependent on the feed rate whereby the use of lower

eed rate produced better surface finish. It was also deter-ined that the surface roughness values obtained increasedhen the cutting speed was increased. Higher surface rough-ess values at higher cutting speeds can be explained byhe highly ductile nature of austenitic stainless steels, whichncreases the tendency to form a large and unstable built updge (BUE). The presence of the large and unstable BUE causesoor surface finish. Wear at the cutting edge directly influ-nces the machined surface roughness since the edge is in

irect contact with the newly machined surface (Ezugwu andim, 1995).

Table 3 – Comparison of kinematic viscosity of the three cutting

S. no. Temperature( ◦C)

Viscosity (mPa S)of soluble oil

1 40 1.632 50 1.043 60 0.89

Coefficient of thermal expansion Mm m−1 ◦C−1 17.8Thermal conductivity W/mk 16.2Specific heat capacity J/kg K 500

1.2. Austenitic stainless steel

Austenitic stainless steels are characterized by a high workhardening rate, low thermal conductivity and resistance tocorrosion (Groover, 1996). Stainless steels are known for theirresistance to corrosion. But their machinability is more diffi-cult than the other alloy steels due to reasons such as havinglow heat conductivity, high BUE tendency and high deforma-tion hardening (Kopac and Sali, 2001). Many attempts havebeen made to improve the machinability of austenitic stain-less steels (O’Sullivan and Cotterell, 2002). It was reported thataustenitic stainless steels are difficult to machine (Akasawa,2003). Problems such as poor surface finish and high toolwear are common in machining of austenitic stainless steel(Kosa, 1989). Ihsan et al. (2004) carried out turning tests onAISI 304 austenitic stainless steel to determine the optimummachining parameters. Zafer and Sezgin (2004) determinedthe best suitable cutting condition for machining of AISI 304stainless steels by considering the acoustic emission duringthe cutting process. The best cutting speed and feed ratewere determined according to flank wear, BUE, chip form,surface roughness of the machined samples and machinetool power consumption. It was concluded that, the low-est flank wear is observed at a feed rate of 0.25 mm/revfor all the cutting speeds. Tables 1 and 2 show the chem-ical composition, physical and thermal properties of AISI304.

1.3. Cutting fluids

Cutting fluids have been used in the machining process withthe purpose to improve the tribological characteristics of thework piece–tool–chip system. It is interesting to note that theuse of coolants for machining was first reported by Taylor in1907, who achieved up to 40% increase in cutting speed whenmachining steel with high speed steel tools using water as

face finish, improved dimensional accuracy, reduced cuttingforce and reduced vibrations (De chiffre, 1988). Cutting flu-

fluids

Viscosity (mPa S)of coconut oil

Viscosity (mPa S) ofstraight cutting oil

26.8 45.720.3 28.215.46 19.5

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Table 4 – Critical parameters and their levels

S. no. Machining parameter Unit Level 1 Level 2 Level 3

1 Cutting speed, Vc m/min 38.95 61.35 97.382 Depth of cut, d mm 0.5 1.0 1.23 Feed rate, f mm/rev 0.2 0.25 0.28

duced better results than the commercially available mineraloil in terms of tool life improvement and reduction in thrustforce.

Table 5 – Experimentation and observations

S. no. Vc d f D (�) Vb Ra

1 38.95 0.5 0.2 C (26.8) 0.045 1.912 61.35 1.0 0.25 S (1.63) 0.096 2.493 97.38 1.2 0.28 St (45.7) 0.134 3.164 38.95 1.0 0.25 S (1.63) 0.075 2.305 61.35 1.2 0.28 St (45.7) 0.107 3.296 97.38 0.5 0.2 C (26.8) 0.071 2.117 38.95 1.2 0.28 St (45.7) 0.097 3.018 61.35 0.5 0.2 C (26.8) 0.055 2.069 97.38 1.0 0.25 S (1.63) 0.126 2.46

10 97.38 0.5 0.25 St (45.7) 0.104 2.4311 38.95 1.0 0.28 C (26.8) 0.081 2.4712 61.35 1.2 0.2 S (1.63) 0.085 2.5913 97.38 1.0 0.28 C (26.8) 0.106 2.6514 38.95 1.2 0.2 S (1.63) 0.068 2.3215 61.35 0.5 0.25 St (45.7) 0.095 2.5916 97.38 1.2 0.2 S (1.63) 0.105 2.5117 38.95 0.5 0.25 St (45.7) 0.098 2.2518 61.35 1.0 0.28 C (26.8) 0.095 2.6119 61.35 0.5 0.28 S (1.63) 0.094 2.9220 97.38 1.0 0.2 St (45.7) 0.10 2.3521 38.95 1.2 0.25 C (26.8) 0.077 2.3322 61.35 1.0 0.2 St (45.7) 0.069 2.4623 97.38 1.2 0.25 C (26.8) 0.105 2.5124 38.95 0.5 0.28 S (1.63) 0.076 2.6825 61.35 1.2 0.25 C (26.8) 0.088 2.4626 97.38 0.5 0.28 S (1.63) 0.10 2.9227 38.95 1.0 0.2 St (45.7) 0.060 2.14

4 Type of cutting fluid, D –

ids provide lubrication between the work piece and tool andalso remove heat generated during the metal cutting pro-cess (De Chiffre et al., 1994). The chemical composition andmechanical properties of the work material, the tool and thecutting fluid are of vital importance in determining processperformance and finished surface quality. For applicationswhere a metalworking fluid with better lubricating propertiesis needed, a non-water-miscible fluid may be recommended.In other cases with high cutting velocities, a water-misciblefluid is often preferred due to its better cooling properties(Kajdas, 1989). But application of conventional cutting fluidscreates several techno-environmental problems. Environmen-tal pollution due to chemical dissociation/break-down of thecutting fluid at high cutting temperature, biological (derma-tological) problems to operators coming in physical contactwith cutting fluid, water pollution and soil contamination dur-ing disposal. The use of conventional petroleum-based cuttingfluids is potentially dangerous. The effects of a particular cut-ting fluid on mankind, working environment, the work pieceand machine tool as well as generally on living environmentas a whole are usually expressed by their ecological parame-ters. Machine operators are affected by contact with varioussubstances within the cutting fluids (Sokovic and Mijanovic,2001).

1.4. Vegetable-based cutting fluids

Cutting fluids based on mineral oils are traditionally used inproduction shops due to their chemical stability and frequentreuse. However, the present trend towards new types of cuttingfluids based on vegetable oils and esters in machining is clearlyjustified by their higher biodegradability and lower environ-mental impact. Emulsions of vegetable oils were preparedusing ionic and non-ionic surfactants for use as metal workingfluids. Over the years, vegetable oils and fats have been usedand retained their importance as metalworking lubricants.Most attention has been given to vegetable oil-based emul-sions, and few references are available on these emulsions asmetalworking fluids. The use of vegetable oil in metalwork-ing applications may alleviate problems faced by workers,such as skin cancer and inhalation of toxic mist in the workenvironments. Jacob et al. (2004) developed a vegetable-basedemulsion that can be used in the metal working industry toreplace partially or completely the commonly used petroleum-based emulsions. Vegetable oils have good lubricating abilityand have been used for the formulation of metal cutting emul-

sions (Herdan, 1999). Vegetable oil-based emulsions were alsoa part of recent research to produce stable emulsions to useas metalworking fluids and in other applications (Alanderand Warnheim, 1989). Ioan et al. (2002) presented the first

Coconut oil Soluble oil Straight cutting oil

experimental results on lubricating capacity of rape seed oilcompared to that obtained for a usual mineral oil. Belluco andDe Chiffre (2002) made an investigation on the effect of newformulations of vegetable oils on surface integrity and partaccuracy in reaming and tapping operations with AISI 316Lstainless steel. Cutting fluid was found to have a significanteffect on surface integrity and thickness of the strain hard-ened layer in the sub-surface, as well as part accuracy. Cuttingfluids based on vegetable oils showed better performance thanmineral oils. The efficiency of six cutting oils was evaluatedin drilling AISI 316L austenitic stainless steel using conven-tional HSS-Co tools by measurements of tool life, tool wear,cutting forces and chip formation. All vegetable-based oils pro-

Vc: cutting speed in m/min; d: depth of cut in mm; f: feed rate inmm/rev; D: type of cutting fluid; Vb: flank wear in mm; Ra: averagesurface roughness in �m; C: coconut oil; S: soluble oil; St: straightcutting oil; �: viscosity in mPa S.

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Table 6 – ANOVA for surface roughness

S. no. Factor Degree of freedom Sum of squares Mean squares Variance % contribution

1 Cutting speed, Vc 2 0.09 0.05 0.575 9.892 Depth of cut, d 2 0.13 0.07 0.805 14.293 Feed rate, f 2 0.56 0.28 3.218 61.544 Type of cutting fluid 2 0.13 0.07 0.805 14.29

0.911.56

1

ClaaawbsotTniaootoooaboCoCppc

2

A

d

S

T

5 Total 86 Error 18

.5. Coconut oil

oconut oil belongs to unique group of vegetable oils calledauric oils. Chemical composition of coconut oil includes lauriccid (51%), myristic acid (18.5%), caprilic acid (9.5%), palmiticcid (7.5%), olcic acid (5%), capric acid (4.5%), stearic acid (3%)nd linoleic acid (1%). Coconut oil is one of the vegetable oils,hich remains as a white crystalline solid at temperatureelow 20 ◦C. More than 90% of fatty acids of coconut oil areaturated. The iodine value of coconut which is a measuref un-saturation in coconut oil is 7–12. The saturated charac-er of the oil imparts a strong resistance to oxidative stability.he specific density of coconut oil is 0.93 g/cm3 and the Cetaneumber is 37. The flash point and viscosity index of coconut oil

s 294 and −130, respectively. Jayadas and Prabhakaran (2006)nalyzed and compared the cooling behavior, thermal andxidative stabilities of coconut oil with sesame oil, sunfloweril and a mineral oil (Grade 2T oil). The thermal and oxida-ive stabilities were determined from the onset temperaturef decomposition. Onset temperature of thermal degradationf coconut oil is lower compared to sunflower oil and sesameil whereas the onset temperatures of oxidative degradationre comparable. It had been concluded that coconut oil showsetter oxidative stability in comparison to other vegetableils with high percentage of unsaturated fatty acid content.oconut oil showed comparatively lesser weight gain underxidative environment among the vegetable oils considered.oconut oil has very high pour point (23–25) because of theredominantly saturated nature of its fatty acid constituentsrecluding its use as base oil for lubricant in temperate andold climatic conditions.

. Experimental procedure

Centre Lathe (Kirloskar make Turn Master 40) was used for con-

ucting the experiments. AISI 304 was used as the work material and

andvik’s carbide CNMG 12 04 08 insert was used as the cutting tool.

he inserts were clamped mechanically on a rigid tool holder DCLNR

Table 7 – ANOVA for tool wear

S. no. Factor Degree of freedom Sum of s

1 Cutting speed, Vc 2 0.00132 Depth of cut, d 2 0.00033 Feed rate, f 2 0.00114 Type of cutting fluid 2 0.00015 Total 8 0.00296 Error 18 0.0080

– – –0.087

2525 M12. After the machining process, the insert was removed and its

flank wear was measured using Mitutoyo’s Tool Maker’s microscope.

To understand more about the tool wear the microscopic picture of

inserts were observed using Carl Zeiss optical microscope, having mag-

nification range of 500×. The average surface roughness on the work

piece was measured using Mitutoyo’s Surftest surface finish measuring

instrument. The experimentation for this work was based on Taguchi’s

design of experiments (DOE) and orthogonal array. A large number of

experiments have to be carried out when the number of the process

parameters increases. To solve this task, the Taguchi method uses a

special design of orthogonal arrays to study the entire parameter space

with a small number of experiments only. In this work, three cutting

parameters namely, cutting speed, depth of cut and feed rate were con-

sidered for experimentation. Along with this, the type of cutting fluid

used, is also considered as one of the critical input parameters while

designing the experiments. Table 3 shows the kinematic viscosity of

the three cutting fluids considered in this work at various temperature.

Accordingly there are four input parameters and for each parameters

three levels were assumed. For a four factors, three level experiment,

Taguchi had specified L27 (3)4 orthogonal array for experimentation.

The response obtained from the trials conducted as per L27 array

experimentation was recorded and further analyzed. Table 4 shows

the parameters and their levels considered for the experiments. Cut-

ting fluid is one of the parameters that does not have any quantitative

levels but each oil is being considered as one level for experimenta-

tion. Table 5 shows the actual cutting parameters used for each trial of

experiment and the corresponding values of observed Vb (flank wear)

and Ra (average roughness value of surface finish) obtained.

3. Analysis of variance (ANOVA)

The observed values of tool flank wear (Vb, mm) and surfaceroughness (Ra, �m) were used for determining the significantfactors influencing the machining process. The significantparameters influencing the surface roughness and tool wear

were found using the ANOVA procedure. Tables 6 and 7 showthe ANOVA for surface roughness and tool wear, respectively.From the calculations it is being inferred that feed has moreinfluence on surface roughness and cutting speed has more

quares Mean squares Variance % contribution

9 0.000695 1.562 46.490 0.000150 0.337 10.036 0.000580 1.303 38.734 0.000070 0.157 4.659 – – –1 0.000445 – –

904 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 9 ( 2 0 0 9 ) 900–909

conu

Fig. 1 – Feed rate vs. surface roughness. (1) Co

influence on tool wear. Further it is also being inferred thatcutting fluid has considerable influence on both the processparameters, i.e. on Vb and Ra. Model calculation for determin-ing the percentage influence of each cutting parameters onsurface roughness is being presented in Section 3.1.

3.1. Model calculation of ANOVA for surface roughness

A model calculation for determining the percentage contri-bution of one cutting parameter on surface roughness isbeing presented here. In the first step, the overall mean wascalculated which was the average of the surface roughness

Fig. 2 – Feed rate vs. surface roughness. (1) Coconut oil, (2) solub[constant]; cutting speed (Vc): 38.95 m/min, 61.35 m/min and 97.3

t oil, (2) soluble oil and (3) straight cutting oil.

measured during the trials. The subsequent steps were self-explanatory

overall mean (m) :127

∑ ´�i = 1

2767.98 = 2.52

grand total sum of squares =∑ ´

�2

i = 173.93

sum of squares due to mean

= number of experiments × m2 = 171.46

le oil, (3) straight cutting oil; depth of cut (d): 0.5 mm8 m/min at the three points a, b and c, respectively.

j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 9 ( 2 0 0 9 ) 900–909 905

F le oilf ee po

wwSourso

m

v

ig. 3 – Cutting speed vs. tool wear. (1) Coconut oil, (2) solubeed rate (f): 0.2 mm/rev, 0.25 mm/rev, 0.28 mm/rev at the thr

total sum of squares = grand total sum of squares

−sum of squares due to mean = 2.47

sum of squares due to cutting speed

= 3[(A1 − m)2 + (A2 − m)2 + (A3 − m)2] = 0.0906

here A1 is the average surface roughness value observedhen the first level of cutting speed was used for machining.imilarly A2 and A3 are the average surface roughness valuesbserved when the second and third level of cutting speed wassed for machining. The sum of squares due to each of theemaining three factors are calculated using similar relation-hips and found to be 0.13, 0.56 and 0.13 for the factors depthf cut, feed rate and the type of cutting fluid, respectively.

degree of freedom for the error

= degree of freedom for the total sum of squares

−sum of degrees of freedom for various factors

= 26 − 8 = 18

ean squares = sum of squares due to each factordegrees of freedom for each factor

ariance ratio = mean squares due to the factormean squares error

percentage of contribution

= sum of squares for each factor × 100total sum of squares

= 0.09 × 1000.91

= 9.89 for cutting speed.

, (3) straight cutting oil; depth of cut (d): 0.5 mm [constant];ints a, b and c, respectively.

Similarly, the percentage contribution of the other threecutting parameters, viz. depth of cut, feed rate and cut-ting fluid on surface roughness was evaluated. The resultsof the ANOVA for surface roughness were summarized inTable 6.

4. Mathematical modeling

Multiple linear regression models were developed for flankwear and surface roughness using Minitab-15 software. Theresponse variable is the flank wear and the surface roughness,whereas the predictors are cutting speed, feed rate, depth ofcut and the viscosity of the cutting fluids. The viscosity ofeach cutting fluid at 40 ◦C was considered for the mathemat-ical modeling. Accordingly the equations of the fitted modelfor flank wear and surface roughness is given below.

Vb = 0.00052Vc + 0.0194d + 0.336 f + 0.000069� − 0.0459

Ra = 0.00280Vc + 0.299d + 6.87f + 0.00067� + 0.376

where Vb is the flank wear in mm, Vc is the cutting speed inm/min, d is the depth of cut in mm, f is the feed rate in mm/rev,Ra is the surface finish in �m and � is the viscosity in mPa S.

5. Results and discussions

5.1. Performance of coconut oil with respect to surfaceroughness and tool wear

The technological tests to assess the performance of cutting

fluids were carried out on a turning process with recording ofthe important observations such as, cutting forces and wearof tools, temperature of work piece and tool insert, chip shapeand color of chip, surface quality obtained and vibrations of

906 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 9 ( 2 0 0 9 ) 900–909

ondi

Fig. 4 – Microphotographs of tool wear. Machining c

machine tool, cutting tool and work piece. In this work, onlytwo parameters namely tool wear and surface roughness wasconsidered to understand the performance of coconut oil as ametal working fluid when machining Stainless steel AISI 304.From the ANOVA table for surface roughness, it was foundthat feed rate (61.54%) is the most significant parameter, whichaffects the surface roughness of AISI 304 material while turn-ing. The surface roughness variation at different feed rateswas compared for various cutting oils. Experiments were con-ducted by varying the feed rate, keeping the other parametersnamely cutting speed and depth of cut constant at 90 m/minand 1 mm, respectively for each oil individually and graph was

plotted between feed rate and surface roughness. Fig. 1 showsthe plot between the feed rate and surface roughness obtainedduring the turning process in the presence of each cuttingfluid. It was observed that the surface roughness increases as

tion: Vc, 38.95 m/min; d, 0.5 mm and f, 0.25 mm/rev.

the feed rate increases and the surface roughness on the workpiece is less in the case of coconut oil at all the feed rates. Asthe feed rate is increased from 0.1 mm/rev to 0.355 mm/rev,it is observed that soluble oil starts off with a lower surfaceroughness almost equivalent to that of coconut oil. But as thefeed rate increases, the increase in surface roughness value ishigh in the case of soluble oil and straight cutting oil. Coconutoil gives better surface finish at every feed rate and the sur-face roughness obtained with coconut oil is much lower thanthat obtained with other cutting fluids. Further experimentswere carried out by varying all the three cutting parameters foreach cutting fluids and the process parameter values (surface

roughness and tool wear) were recorded. From the recordedvalues Figs. 2 and 3 were plotted between surface roughnessVs feed rate and tool wear Vs cutting speed. From the graphsit is being inferred that for any combination of cutting param-

j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 9 ( 2 0 0 9 ) 900–909 907

nk w

efl

5c

Tf

Figs. 5–10 – Surface plots, Ra: surface roughness, Vb: fla

ters coconut oil always outperform the other two cuttinguids.

.2. Microscopic study of tool wear occurring on

arbide tool

he extent of flank wear is considered a dependable criterionor judging the life of the cutting tool. In case of carbide tools,

ear, d: depth of cut, Vc: cutting speed and f: feed rate.

through proper alloying of tungsten carbide with titanium andtantalum carbides, sufficient resistance to crater is obtainedso that most tools do not fail by cratering, before a reasonableamount of flank wear is obtained on the flank of the tool. The

flank wear can be more easily observed and measured thanother types of wear and it is relatively easy to predict. Thedevelopment of flank wear initially involves a high rate fol-lowed by a more or less linear trend and finally rises rapidly

n g t

r

908 j o u r n a l o f m a t e r i a l s p r o c e s s i

when the amount of wear crosses beyond the critical value.To understand more about the tool wear the microphotographof inserts were observed using Carl Zeiss optical microscope,having magnification range of 500×. The flank was developedwhile machining at certain cutting parameters (cutting speed:38.95 m/min, depth of cut: 0.5 mm and feed rate: 0.25 mm/rev)in the presence of coconut oil is shown in the microphotograph(Fig. 4). And for the same cutting condition, the microphoto-graph obtained on the insert when the other two cutting fluidswere used was also presented.

The microphotograph taken at 100× and 200× shows theflank wear caused while machining at lower cutting speed.The figure shows the tool tip where the maximum wearing hadoccurred. In the case of coconut oil, the tool wear is consider-ably less when compared to soluble oil and straight cutting oilat lower cutting speed. Moreover, the viscosity of coconut oilis more than that of soluble oil and less than that of straightcutting oil, which favors easy flow of cutting fluid at minimaloil condition. This enables the reduction of friction betweenthe tool and work piece, and easy removal of heat developedat the interface. The heat removal at lower cutting speed givescoconut oil a considerable advantage than that of soluble oiland straight cutting oil. At lower speeds, coconut oil yieldslower wear and produces good surface finish when comparedto other cutting fluids.

5.3. Surface plots

A graphical analysis was done on the observed values usingMinitab software. The response surface plots obtained for eachprocess parameter with respect to the cutting parameters isbeing presented. Figs. 5–10 show the estimated response ofsurface roughness and tool wear for the cutting parametersnamely cutting speed, depth of cut and feed rate. Fig. 5 showsthe estimated response of surface roughness for the corre-sponding cutting speed and depth of cut. It is seen that cuttingspeed has significant effect on surface roughness. As has beenpreviously pointed out, this figure shows cutting speed around80 m/min gives the lowest surface finish. Ra value is almostconstant for lower depth of cut, but the increase is seen forhigher values. Fig. 6 shows the estimated response of surfaceroughness for the corresponding cutting speed and feed rate.From the graph, it is seen that feed rate has the most sig-nificant effect on surface roughness and its variation is veryhigh when compared to other parameters. Fig. 7 shows theestimated response of surface roughness for the correspond-ing feed rate and depth of cut. It is established that feed ratehas the highest impact on surface roughness. Fig. 8 showsthe estimated response of tool wear for the correspondingcutting speed and feed rate. Initially, the tool wear increasesslightly with the increase in cutting speed and it remains con-stant for cutting speed around 60 m/min. Beyond that, toolwear increases linearly with the increase in cutting speed.Fig. 9 shows the estimated response of tool wear for the cor-responding cutting speed and depth of cut. From the graph,it is confirmed that depth of cut has the least significance

on tool wear and cutting speed has its domination on toolwear over feed rate and depth of cut. Fig. 10 shows the esti-mated response of tool wear for the corresponding feed rateand depth of cut. For higher values of feed rate and depth of

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cut, the tool wear is considerably high and it is constant forlower values.

6. Conclusions

Experiments involving cemented carbide tool inserts andAISI 304 stainless steel work material under varying machin-ing parameters and with three different cutting fluids wereperformed. Cutting fluids were considered as importantparameters in the machining process along with cuttingspeed, feed rate and depth of cut. An analysis of variance(ANOVA) was made and it was found that feed rate hasgreater influence on surface roughness (61.54% contribution)and cutting speed has greater influence on tool wear (46.49%contribution). Further it was found that cutting fluid has someconsiderable influence on both surface roughness and toolwear. Effectiveness of the cutting fluids in reducing the toolwear and improving the surface finish was found by compar-ing the relative performance. In general, coconut oil was foundto be a better cutting fluid than the conventional mineral oilsin reducing the tool wear and surface roughness. Surface plotswere drawn between the various process parameters so asto understand more about their individual relationship andrelative contribution to surface roughness and flank wear.

e f e r e n c e s

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